BJ's Wholesale Club (you need to pay to get in) - $40 for Gran Turismo 4
If you pay for a day pass to go in, I think it is like $15. They have lots of other goodies like Prince of Persia w/guide for PS2 for $20, Ratchet & Clank 2 w/ guide for PS2 for $22, and several other games with their corresponding guides. I think they had Final Fantasy X-2 with its guide for $20 as well, and I just saw a post where someone said they got Arc The Lad TS for PS2 for $2.99 or something there.