How much does stained glass cost?

It varies from reasonably inexpensive to quite expensive. Just depends what type it is and sometimes what colour. Some colours require expensive minerals and that jacks up the price of those colours(usually red or pink). I think your best bet is to go to a stained glass store and see what kinds you have, how much they're worth, and go from there. Keep in mind that small pieces, less than about 6" x 6", are basically scrap because they aren't big enough for many projects. I used to do a lot of stained glass and kept small pieces around for a while but rarely found any of them useful. Fiddling around cutting tiny pieces from merely small pieces takes time.