I think this is an awesome DIY project. I personally haven’t seen any silver quarters for years, but you can still pick them up if you keep your eyes peeled. American quarters (25cents) before 1964 were made from 90 percent silver and if you wanted a bigger sized ring a Kennedy half dollar before 1964 would work too.
Realistically you are looking at a maximum ring size of 7 with a quarter and probably up to a 10/11 with a Kennedy dollar. You can always make the quarter ring bigger but it will be thinner. Either way, I think this is a great project if you don’t have a lot of money for a decent sized silver ring. Check it out: