in case it's helpful, I combined this instructables post with a tilt mechanism similar to this to make a removable drawing surface for my existing desk.
The tutorial uses just a drill and screwdriver, but the beefier tilt mechanism would need at least a hand saw and another hinge.
I've found the speedball clips are helpful to keep the surface at the desk edge but tbh an L shape (see carving bench hook below) would probably work just as well if you have the supplies/ability to make it I added the (very basic) tilt brace as I like to put a bit more weight on the surface than the clamps liked while leaning forward but ymmv etc
I used thinner mdf since was cheap enough for a prototype and we have tools and space to use them. It's not pretty but it works well.
The effort/time/money scale really depends on what tools you already have - less than "now bring our your 19th c loom" and more than buying ready-made).