Im looking to sell some games to game-stop so i can get madden 10?

Here's what im selling for credit. Its all in perfect condition. Civilization Revolution, Mercenaries 2, Ghostbusters, Halo 3, Endwar, ins creed, and the darkness. And halo wars. does anyone have any idea what illl get for it. Please dont post something saying gamestop are cheap s i already know