Billy doesn't seem to have a surfboard in Hawkins. I'm assuming he had one (or more) in California. Did Neil make him sell it? Did he sell it without even consulting Billy? (Neil probably pocketed that money regardless, right?) Surfboards are expensive...
Alternatively, the idea he sold his surfboard(s) to buy the Camaro (probably second-hand then if it's a 1979 model), since it also represents his freedom.
Also, I'm just now thinking about the similarities between a surfboard and a skateboard, the skills and the fun of it, and how that could even have been something that connected Max and Billy. But now Max can still do the thing she loves while Billy can't. Brings new texture to Billy constantly telling her that she's skating home, and the implication that he broke her skateboard after she lied to him.
Thank you for sending this in! Excellent questions and thoughts, and there are SO many layers to dig into here. Let's not waste any time and just jump right in. I'm breaking this down into sections, which I hope will be helpful.
How Much Does Billy's Camaro Cost (and when did Billy get his car)?
Billy has a 1979 z28 Camaro, which cost ~$6,000 brand new in 1979. The general depreciation value of cars is a 30% depreciation in the first 2 years and then 8-12% depreciation with every subsequent year.
Now, let's say with reasonable plausibility that Billy buys his Camaro in 1984, sometime before the move in October 1984. Billy's 17 at this point. California did not yet pass its GDL law (that passes in 1997 and goes into effect in 1998). This means that Billy could have applied for a driver's permit as early as 15 1/2 (and knowing Billy, I think he applied for that immediately). He would only be required to hold that learner's permit for 30 days before he could take a driving test and get his driver's license. This means Billy could have had his driver's license as early as the end of October 1982 or beginning of November 1982. That doesn't mean he has a car yet, but it means he can drive independently and without adult supervision.
Billy is a teenager, so he's working part time to save up for a car. There's age breakdowns for how many hours he could work until he's 16. He could also be working under the table with odd jobs for people. Regardless, we must remember that Billy's still at school, he's still a teenager, and he won't be able to work full time. As a result, it will take time for Billy to save up that kind of money working part time/odd jobs. If we follow the idea that Billy finally gets a car in 1984 (which is a two year period between the point at which Billy can drive), and apply the depreciation value of the Camaro, we're looking at a cost of roughly $2,863 - $3,271 for the 1979 Camaro in 1984. A reasonable rounded estimate for what Billy would need to save is about $3,000.
How Much Do Surfboards Cost in the 1980s?
Surfboards are expensive, but they're not 1979 z28 Camaro expensive. I went digging to find costs of surfboards in the 70s and 80s, and found some examples. The first example comes from a Gordon & Smith (San Diego based) ad I found, and the remaining examples comes from recollections of folks who purchased surfboards in America in the 1960s-1980s:
1967 - A Gordon & Smith Ad from 1967 shows a Midget Farrelly V-Bottom that cost $165
1970 - 5'6" Sam Egan Surfboard purchased for $90 (USED)
1972 - 7' Surfboard purchased for $120 (NEW)
1975 - Morning Star Surfboard purchased for $140 (NEW)
1976 - 6'10" Crozier Surfboard purchased for $105 (NEW, CUSTOM)
1978 - 5'10" Twin Fin Sam Egan Surfboard with Fin Boxes purchased for $235 (NEW)
1978 - 6'6" Paul Gravelle Surfboard purchased for $180 (NEW, CUSTOM)
1980 - Paul Gravelle Surfboard purchased for $210 (NEW, CUSTOM)
1981 - 6'3" Mark Virgo Surfboard purchased for $180 (NEW)
1983 - 5'3" Crystal Curl purchased for $125 (NEW)
I included a range of years between Billy's lifetime up until 1983 for us to have a general feel for inflation and cost of product over the years. I also included prices of brand new boards, brand new custom boards, and used boards. This will give you an idea of different avenues Billy could take to get a board.
Reasonably speaking, Billy could be spending between $100-200 for a brand new surfboard. He could possibly pay less than $100 for a used board. Given what we know about Billy's clothes and shoes (for example, how Billy wears the unbranded shoes that are the cheaper options, read more here), we must consider the fact that there's a high probability he might go for a used board. Even if he purchased a new board, Billy would need quite a number of surfboards to sell (and remember, he would never get what he originally paid for) in order to get a few thousand dollars to pay for a Camaro. In short...
Would Billy be able to sell a surfboard (or a few) and have the equivalent buying power to purchase a used 1979 Camaro exclusively from the sale of surfboard(s) alone?
No. I think it's also worthy to point out that given Billy's financial situation and what little possessions he does have, I don't think Billy's walking around with, say, 10 surfboards. I think it's more reasonable to consider that Billy definitely has one surfboard, maybe 2.
What other factors must we consider?
We don't just see the absence of a surfboard amongst Billy's possessions. We see an absence of ANY sign that Billy surfed at all. This means that Billy either sold or had to get rid of not only his surfboard, but also his other supplies (i.e. a wetsuit, wax, any fins he bought for an upgrade, etc.).
I'd also like to take a moment to stress what this is like psychologically for a teenager to have to part ways with something they love. We know that Billy loves to surf. We know that surfing holds his happiest memories. It's not just Billy having to part with a sport he loves; Billy's parting with his happiness-- the one positive memory he has in his life. It's reasonable, also, to conclude that surfing was tied up in Billy's identity and how he saw himself. It's also part of his perceived thoughts of his own personal agency and freedom. Having to sell that (either because he was moving or because Neil forced him to get rid of his surfing gear) is selling part of himself. When we consider Neil's abuse, he is not just physically abusing Billy. Neil also manipulates, gaslights, emotionally abuses, verbally abuses, psychologically abuses, emasculates, isolates, intimidates, parentifies, verbally threatens, and economically abuses Billy. So, Neil forcing Billy to get rid of his surfing gear falls right in line with a psychological and emotional abuse with the express intent to isolate and devalue Billy and what he holds dear, as well as revoke any sense of agency Billy feels that he has over his life.
So, How Did Billy Afford his Camaro?
I think it is reasonable to conclude that he was definitely working a part time job to be able to save up for a car. I think it took several years for him to save up that kind of money. While he could have sold his surfboard to contribute to the money he was already saving to buy a car, he could not do an even swap, if you will, meaning that he couldn't sell his surfboard and then immediately go and buy a car. The monetary value just isn't there. It's not even close.
Other factors to consider are:
Billy could have saved up some of the money and Neil gave some of his own money to buy the Camaro. This would set up a scenario whereby Billy would be financially in debt to Neil. He'd need to pay Neil back, and given Neil's tactics, I could easily see Neil setting this up with requiring Billy to pay interest as a way to learn "responsibility" but have it quickly fall down a slippery slope of financial abuse. It would be very easy for Neil to use these car payments (with interest) as a way to reduce Billy's ability to have any type of savings that he could use to get away from Neil. This would be Neil's way of holding power over Billy and his car, thereby reducing the level of freedom Billy really has with his car. Remember, we don't know why Billy didn't leave right away once he turned 18 and graduated from Hawkins. A reasonable conclusion is money and/or Max. Billy could be working to save up enough money to leave, while also having to pay back Neil for debt on the car, etc.
Co-signing titles with cars. In California at this time, 17 year olds could, in fact, be listed on the title of cars, with an adult co-signer. With this set up, Billy does not have sole ownership of the car, but he does carry some more responsibility for it as opposed to his name not being on the title at all (and remember, Neil is trying to force respect and responsibility onto Billy). I could see Neil using a co-signing option because it 1) still shows that Neil is in power over Billy and his car, but in such a way that is dangling freedom-- Billy is almost there in sole ownership, but not quite and 2) can be used by Neil as an excuse for blaming Billy or holding Billy responsible if things go wrong with the car.
Given that, what happened to Billy's surfboard and gear?
Because I don't see a financial possibility for selling a surfboard(s) for a car, I think the most plausible reason why we don't see any of Billy's surfing gear in the series is that Neil forced him to sell/get rid of his surfing gear (and other belongings, particularly ones that would be "burdensome" for a move) before the move. I don't see Billy being able to keep that money for his own use, unless Neil set this up as something like Billy was responsible for moving himself to Hawkins. Billy could have sold his belongings to limit the amount of items he had to move and also financially cover driving the distance to Hawkins. A drive from San Diego to Indiana is over 2,000 miles. Billy's Camaro gets between 12-16 MPG combined. Gas cost (on average) $1.13-1.21 per gallon in America in 1984. If we're generous and say that Billy's car gets 16 MPG the whole way through, he'd need 125 gallons of gas to get to Hawkins. That's about $141.25 - $151.25 just in gas, let alone the cost that Billy would need for another oil change (cars are good for 3,000 miles before another oil change) and other standard wear on his car. How good were his tires at the start of the trip, for example? Were they already running on low tread? Does he need to get new tires? The list goes on and on.
The Similarities between Max and Billy's Sports
Billy and Max are actually far more aligned with their chosen outdoor sports, and I don't think it gets talked about enough! They're both outdoor sports. They both require similar skills. Could Billy have perhaps taught Max how to have better balance? Maybe she was learning a trick on her skateboard, and Billy used his surfing skills to teach her? We know from the VR game that Billy looked after Max when she got all cut up from skateboarding, showing her how to bandage herself up (because nobody was going to do that for her- which is Billy teaching Max from his experience).
Their respective sports are also an easy way to bond without always having to be right up against each other or feel like they're chained to each other, like Neil fosters when they move to Hawkins. For example, Billy can take Max to the skatepark, which is close to the beach. She skates; he surfs, and they go home. It also provides a way for them both to be out of the house, which Billy knows not to be safe.
While the community dynamics of surfing and skating are different, there is much culturally that unites them. As a result, I agree that there are tie ins there that potentially bonded Billy and Max more organically and without the feeling that Neil was forcing them to bond.
And interestingly enough, the tie ins with surfing and skating culture is represented in canon. In S5, Max wears a yellow Ocean Pacific Shirt (OP shirt). Visually and stylistically, we see SO MUCH of Billy in her in S5- from the shirt to the necklace to her hair. Just look at the evidence and also pair that with Max's crash out after losing to a D&D game (she's never learned how to emotionally regulate, either, and it's showing in her behavior). BUT that is a meta for another day.
The thing I really want to stress as it relates to this meta is Max's Ocean Pacific Shirt. Ocean Pacific started out as a surfboard shop in San Diego (where Max and Billy are from), then morphed into selling shirts in the early 1970s to embody SoCal surfer culture. That eventually morphed into Ocean Pacific reaching out to other outdoor sports with their clothing brand (think skateboarders and BMX).
Ocean Pacific actually credits itself as uniting the surfer and skateboarder culture (as well as all outdoor sports) during this time. So not only do the sports have tie ins to each other, Max's style definitely leans into this concept of how she keeps Billy with her, perhaps subconsciously or not, in her own wishes of what could have been over their complicated relationship. You can read all about this here.
The Implications of No Surfboard, Billy telling Max to Skate Home, and a Broken Skateboard
As I've previously mentioned, Billy's loss of surfing is a personal loss of his own identity and freedom. When they're in Hawkins, Billy can't surf anymore. And while Max can, she can't forever. Indiana is not California. California has a moderate climate that allows for skateboarding year round. Indiana does not. Billy and Max get to Hawkins at the very end of October. Billy knows that in a few months, Max isn't going to have her outlet anymore, either. When Billy tells her that she has to skate home constantly (whether it's at the arcade or at school) if she's late, it's not just about being late for pick up. (And being late is not good in the Hargrove home if your name is Billy Hargrove, by the way.) It's a warning that she's running out of time to enjoy the thing she loves. Nothing is permanent in life, and Billy knows that because he ran out of time to enjoy the thing he loved (surfing). And if she doesn't skate now, it's going to be too late for her in a few months, too. Max doesn't yet live in that world, but Billy does. And I think it's very important to remember that Billy and Max BOTH do not have healthy communication norms and Billy and Max DO speak in code with each other. This is Billy's own indirect way of warning her that she better skate while she still can.
And now onto the broken skateboard. As we know, the scene set up implies that, after Max lied to Billy at the Arcade, Billy broke Max's skateboard. There's a day between these two scenes, and we don't actually SEE Billy break her skateboard. But we do have some additional contextual evidence when Billy confronts Max at the Byers' house and says, "You know what happens when you disobey me. I break things." The "things" most likely being the broken skateboard from a few days' prior.
But Billy isn't just breaking Max's beloved skateboard and taking away her sport (temporarily). He's briefly taking away her own way of being able to transport herself. He's trying to stop her from going out and hanging with a boy, which Billy knows will set off Neil and subsequently result in Neil beating Billy. Again, Billy and Max both do not have proper and healthy ways to communicate. They both lash out at each other. Billy is trying to warn Max to stay away from something that's going to get him in trouble, and to do so, he mirrors how Neil took away his own sense of freedom and identity: his surfboard.
BUT here's the thing: it's not an exact mirroring of Neil's behavior, and I think that's important. Billy just breaks it; he doesn't take Max's skateboard away. And we see Max fix her skateboard by taping it up to use it again (and it's worthy to note here that Max does get a new skateboard in the later seasons, which nods back to Max treated as the Golden Child with all her branded sneakers and now, a new skateboard).
And I find this to be worthy to highlight. Why? Because Billy knows that Max's skateboard is her only outlet OUT OF THE HOUSE-- a house that is not safe. Billy knows that Max's skateboard is HER only way to transport herself. He still has his car, even if he doesn't have his surfboard. He's not going to completely eliminate Max's only outlet, and he doesn't. Not in the way that Neil did to him. We also know canonically that Billy is the ONLY person who sides with Max's agency, saying she's old enough that she doesn't need a full-time babysitter. Further, canon informs us that Billy literally doesn't care what Max does; he ONLY cares when she starts doing things that could get him in trouble. That's when he intervenes. In short, Billy doesn't want to take away Max's agency in the way that Neil takes away his agency. But he's warning her that it could get to that point if she doesn't stop doing things that will make Neil mad.
And with that thought of Neil getting mad, I must now cite this scene parallel:
The scene from Billy's memory whereby Billy's mom warns, "Dad will be mad," and the fear/concern on her face if they are late while Billy is out surfing vs. the scene where Max comes inside after talking with Lucas with her plan to go outside with him and Billy looking at Max with the same concern/knowledge that what Max is doing (even if it's what she wants to do) will result in: "Dad will be mad". The parallels are wild, from expressions to the fact that Billy and Billy's mom are dressed similarly and in white (see here).
And so, with all of that said, Billy brakes her skateboard. Forces her to slow down. Thinks that maybe she'll take the hint or start putting the pieces together. He doesn't want to completely remove her agency and freedom away in the ways that Neil has done to him. But he has to get his point across, so he breaks it as a warning that things could get much, much worse if she doesn't realize that her actions are going to make Neil mad. And while I don't believe that Neil would hurt Max, he will, as canon reveals, hurt Billy for Max's actions. And if Max keeps it up, how long can Billy stand between her and Neil? The answer? He'll kept standing up (read more here), but it can't last forever. And canonically, it doesn't. Billy keeps standing and taking abuse in all forms-- not just from Neil-- until he's dead.