Grab a bunch of accessories off overstock. It's pretty cheap there. I would assume you only need the harddrive to make it a premium. Unless you're finicky about the wireless controller, headset and 1 month of xbox live gold.
Gamestop won't give you full price for a system or a game. I've tried, and they told me I need to open it before they can take it. At that point, they won't even give you full price.