If your blockbuster has a gamerush, they should have a deal where you trade any game and get a new one for $29.99 PLUS the trade in value of the game. Now since Driv3r just came out, it'll be worth $35 trade-in credit. Through complex science and simple math, you can get Thief for free.
I just traded Chronicles of Riddick using this deal and got Psi-Ops for free. Good times.