how big is the HDD? if its anything over stock than that price is DIRT CHEAP!. ive seen xboxes like that go for $300+
also a mod xbox is totally different from a 360. you can store you games\dvd's on it. play dvd's w\o the remote, use emulators, and you can still play online if the game you want to play is on XBC, which uses your computer interenet connection and the system link feature in the game to have a xbox live kind of thing, but its free.