Well, those aren't going to be regularly stocked at many retail stores, so you're just going to have to hit your local Best Buys and Gamestops and whatever other toy/game and electronics retailers you have locally, and see if they have any. If they have one, it should be $99 or less. I don't really what else there is to say, so, get out there and look.
The Wii plays all Gamecube games, by the way, if you'd rather just get one of those.