These prices could be a YMMV. I picked up Family Guy: Something, Something, Darkside for $4.49 at my local GS.
The price for some of these are stupid though. $11.99 for Spiderman, when it's $10 at Target. Wanted is only $7.99 on Amazon.
If you want to do it with Gamestop, then i would recommend paying for the Gamestop Edge Card. It's about $15 a year, but you get an extra 10% trade in credit on all games/systems/accessories, and you get 10% discount on any used games or accessories that you buy from them.
When my daughter...