AllIn:
It really boils down to this... how much do you value the content? If you don't care, and you just want a lot o' storage space then find the biggest honkin' storage you can (@ 7200 RPMs of course) and use that.
If you value your content start to think about methods of minimizing the impact of a drive failure. When, not if is the question to be asking.
Ideally, I'd like to be able to mount up a network share from a NAS Device and store it there, but that's asking for way too much from Dish
Lacking that, if there was a RAID5 with USB interface, I'd go for that assuming the price was palatable.