Where are you at? I know some folks or a place you might could get rid of them if you're anywhere near Atlanta. Otherwise you might try craigslist, eBay or something like that. If you live near a track, take them up there. If they're almost BRAND new, you might fetch a pretty penny from them. Used and unevenly worn tires will bring down their value significantly. I can find decent tires for about $30. The wheels should still be worth something if they're from a fairly new bike. If they're from an old machine, they're still worth a little; just might be harder to get rid of. All in all, you should be able to get your $100 out of it.

*and yeah, look on the sidewall of the tire for sizes