I went to ebay to check around the ATV sellers, I found it funny how they advertise the "Adult Edition", loaded with porn. and there are a lot fo them.
Anyways, OP, most of the sellers got good feedback so you should be fine if you go that route.
As mentioned before, Jilbreaking and installing app on the ATV is no really that hard, you can save some money doing it yourself, there are almost infinite amount of guide, videos and forums thread about pretty much anything you can do with it.
keep and eye on this website, the usually post the latest news and guide on the Apple tv http://www.appletvhacks.net/