If you are serious and needing something and want to discuss it (in order words I wouldn't just send in questions if you're just curious), you can ask http://www.voxel.net as they specialize in this soft of thing, as do others I'm sure.
Ahhh, well I don't know much about it, however I'd think that...
"How much will one retail for compared against a 1U/2U server?"
It would depend on what you are building. A 2U server could be extremely expensive, even more so than a cluster of 3 servers doing the same job. Not exactly sure what you're asking. Then again, I might be missing a piece of the puzzle.