Picked up a loose cartridge of "Mountain Bike Rally / Speed Racer" for about $12.00 2 weeks ago.
Came across a couple years ago in a PC mom and pop store, someones trade in for new games. They dropped off a sealed boxed Ultima 3 for the AtariST, an opened complete Ultima 3 and 5. I picked it all up for $12.00 Yay!
FYI: I saw online recently that there is a guy selling a copy of "Video Life" complete for $3,000. It's the rarest licensed USA Atari 2600 game ever made as far as i'm aware. It hasn't sold as of 04/21/09 if someone is nuts about gaming enough to grab it.