NCAA College Basketball 2K3 is a sports game released for the Xbox, PlayStation 2 and Nintendo Gamecube. While the Xbox and PS2 versions are easy to find, the Gamecube version is widely considered to be the rarest Gamecube game of all time.
Sega had made a decision to stop releasing sports games for the Gamecube, which had caused this game to stop production really early and as a result it barely made it to store shelves. Being that it's a sports game, what little copies made didn't sell very well.
NCAA College Basketball 2K3 now goes around the $100+ mark and to this day is one of the few sports games out there to be valuable.