This is a question that comes up a lot. I always tell people who are first starting out making coin rings to do so with the “change in your pocket”….. literally.
Start with coins like clad (non-silver) quarters and half dollars, (your local bank will often have the JFK half dollars if you don’t have any). This gives you invaluable experience gained only through practice on the various techniques of coin-ring making and gets you familiar with the process, without worrying about making a mistake on a more expensive silver coin, for example.
As far as using 90% silver coins to make rings, a great place to start is to look up a local coin shop/dealer in your area to get some 90% silver coins. Talk to the owner of the shop; let them know what you’re looking for and why. It’s always good to have some type of report/connection with them, as they could help to answer questions you may have.
Tell them that you want “junk” silver quarters, half dollars, etc. Many shop owners will let you pick through what they have, and you’ll mostly only be paying what the metal content, or “melt value” of the silver coins are; as junk silver coins will not contain any numismatic value.
It’s best to stay away from coins that have “numismatic” value; (or value based on factors such as condition and amount minted) at least when first starting out.
You can also look on eBay for coins, but I recommend going to any of a number of online sites to first determine what the general values of the coins are before buying them.
You can pick up a yearly copy of The “Official Red Book” of Coin Values, as it’s a great resource for knowing what the numismatic value of specific coins are. Go to: https://www.whitman.com/redbook
You can also go to: http://www.CoinFlation.com …. this website will give you an up-to-date pricing on the “melt values” of various coins based on their weight and metal content.
Knowing the basics about coin values and specific metal content will help you tremendously as you begin and continue to make coin rings!