Do you have a quarter from 1964 or before? If you do, it is made of silver. You can turn that coin into a nice silver band using a spoon, a drill, and a metal file.
A quarter will yield a small ring, size ~7 or less. You can get a larger size but the ring will be very skinny. If you want a larger size ring, a Kennedy half dollar will work well. Again, anything 1964 and earlier will be silver.
Optional but recommended
Step 1: Find a Silver Quarter
I was lucky enough to find two silver quarters in my change, but unless you are looking, you may not find one. Any quarter from 1964 and earlier should be silver. They are much lighter in color than newer quarters. I've read you can use the the sandwiched coins, but the metal is harder and it wouldn't be a silver ring. You can also buy one at a coin dealer for a couple dollars.
DO NOT buy an expensive silver coin for this, you will be destroying it.