How much cash could I get for my xbox 360 and games?

[teninchrod]

I was thinking about selling my xbox and all my stuff to get a guitar. How much would gamestop or a similar game store. Here's what I have:

Xbox 360 pro system, all cords with 20g hard drive.
Microsoft Headset (kind that comes with xbox)
White wireless controller
Black wireless controller
Microsoft rechargeable battery station

http://www.gamestop.com/Catalog/ProductDetails.aspx?product_id=43321

Two white rechargeable battery packs
one white rechargeable battery pack

Games:
Skate 2
Unreal Tournament 3
Halo 3
Condemned 2
Civilization Revolution
Call of Duty World at War
Halo 2