It is implied in Crisis Core that the reason why SOLDIER are paid so little is because Lazard was funneling money away from Shinra in an attempt to get his revenge for President Shinra betraying and abandoning his mother. Lazard being relatively young means that he hasn't had this job for long, so SOLDIERs must have used to get paid more.
Which is hilarious because imagine Lazard steeling himself to tell the three legendary 1st Class SOLDIERs that they're getting a pay cut.
But their reactions are not what he expected...
He calls Angeal into his office first, because he supposes Angeal will be the easiest to deal with. As expected, Angeal declares: "I am doing this for honor, not money." Angeal used to live in poverty, his family barely making ends meet, he knows he will still be much better off now. He is skilled at cooking with leftovers, he's still wearing his unmodified Shinra-issued uniform (why wouldn't he, it came free and is surprisingly sturdy), he has a place to sleep, which means he will have enough to buy and care for his plants and still have some money left over to send home to his mother. That's all he needs.
What Lazard didn't expect is a lecture. A two hour lecture about paying 2nd and 3rd class kids fairly and honoring their relentless training and hard work. And above all else, giving them enough to make it possible for them to realize their dreams. Lazard makes a mental note to ask a 2nd or 3rd sometime about this whole dream business.
Next, he calls in Genesis. Genesis might be a problem. First time Lazard laid eyes on Genesis it was immediately clear to him this was a man used to luxury. Lazard wonders whether he could survive a firaga to his face, and considers how best to approach the subject to minimize the chances of an inferno but decides to just get straight to the point. It will be less suspicious. But Genesis just looks confused. Halfway through Lazard's explanation he asks: "We are getting paid for this?" (His parents financed everything he needed, and his paychecks have been accumulating in his account which he didn't even know existed, let alone how to access it.)
Lazard leaves Sephiroth for last. He's nervous and sweating a bit now. If the legendary hero gets offended... Lazard has heard stories.
Sephiroth stands unnaturally still, silent, and Lazard can't help but think of a snake ready to strike.
For a few moments he could swear he sees Sephiroth's pupils getting narrower and narrower. Then Sephiroth speaks: "Will the company still provide my shampoo and conditioner in satisfying quantities?" When Lazard says the pay cut is unrelated to any of the perks he is receiving, without a word Sephiroth turns and leaves.
