Shortage of Twilight Princess for the Gamecube?

This week Nintendo released the Legend of Zelda: Twilight Princess on the Gamecube. Supposedly the game wasn’t going to be too difficult to find since major retailers have were going to have it stocked and Circuit City is discounting it down to $38. Only a few days after the game’s release copies have been popping up on eBay priced around the $70s. Is this really a rare game or is this just another case of Twilight Princess fever?