I've seen a few games going real cheap, an ad on craigslist in houston a few months ago had about 10 going for $20 total, i imagine there's some rare ones but most are commonly available for a cheap price.
I picked up the carts for em at a local good will for 40 cents usd $ a pop no console just 4 carts thought I'd show em to my sega fanatic friend who'd proboaly never herd of em and then crack up laghing as he scratched his trying to figure out what in the heck they were .