How much would gamestop give me for this?

May be...

For a playstation 2 the slim one gently used and guitar hero 3 with game and controller

Actually, gamestop will only give you 30 dollars for your PS2. Also, you must trade in your controller with the PS2 or else they will not take it. I agree that it is a ripoff though. For GH3 they will proabaly give 10-15 dollars total including the guitar. So total, i think you will get around 50 dollars. (Plus if you have an edge card you will get an extra 15%)

A brand new silver slim ps2 cost 99$ and a brand new guitar hero 3 cost 30$ and a dualshock ps2 cotroller cost 15$. So figure they'll give u have of the money its there all worth, 50 for the ps2 ,15 for the game and 7 for the controller so that will be 72 dollars. But being realistic since they usually like to rip people off they'll give u about 50 -60 dollars for everything.