How much will GameStop give me for my Xbox 360 slim?

It's 250gb, everything works on it. I only had it since Christmas last year and just got bored with it. I have the controller, cords, things like that. I also have some games; Halo 3 Forza Motorsport 4 CoD World at War Modern Warfare 3 and minecraft. Also I have a Glowlight headset. I still have the original box the console came in, don't know if that matters or not.

My friend traded in his slim 250gb with box and controllers etc and he got £60, I'd suggest selling it on eBay, could make £100-£120+ easy.

Gamestop is such a ripoff i wouldnt recommend selling anything there you would be lucky to get like 120$ at the most even if that.
Try craigslist or ebay