The chances of getting a silver quarter is really, really low. I've searched a few bags ($300 each or so) of quarters from vending machines (the older type that will take anything, silver, slugs, etc) and never found a single quarter. On the plus side I did manage to fill a full set of US state quarters to that date... But silver quarters are rare, halves are going to be the best for silver, then dimes. Searching quarters just isn't worth it, I've just started checking only pocket change when it comes to quarters, bags simply take too long for how little silver is in circulation.