How much would these games be if i trade in these games?

Since you said Gamestop are doing a thing where if you trade-in three Wii games you get 15 bucks and you are trading in three Wii games so you get 15 bucks for them and then the money back from the Avatar game. That means you get 15 bucks worth of store credit (not including the Edge Card) and about 18 bucks back for the Avatar game.