That aforementioned cord goes for 20 bucks new, but you could find it used, I'm sure. A lot of people bought theirs, used them once, and then either traded them in, or are probably selling them on eBay.

http://www.ebay.com/itm/XBOX-360-GARY-U ... 227wt_1392

It's an offbrand, but it's cheap and looks like it'd work fine.