I went to Gamespot and some of their prices are crazy. But then again, I am a cheap ass too. I wanted SSMB: Melee, but it was over $20 and a Wal-Mart nearby was only selling it for $20 new. Should've gotten it when I had a chance.
I think I saw Paper Mario for $35 and my friend bought it new at Wal-mart for $20. Price gouging! Though some good GC games are fairly cheap. Got Gun for $5, Eternal Darkness for $9 and Viewtiful Joe for $5.
Well if you look at Amazon.com, you will see you can still buy Gamecube games brand new directly from the supplier and not used or from someone else. Like Super Smash Bros. Melee that game is like $30 bucks still brand new, and I saw it at Gamestop for that price used, its just that the retail value is higher than most Gamecube games like the games that don't sell so well.