Pop down to one of the many popular PC mod forums, and hit some of the posts regarding 'build your own box'. Download the ATX specification to get proper sizes for the drive cage area and the PSU, then just make your own box to your own specification. It'll be the cheapest alternative, and you can make it from aluminum, wood, acrylic, etc.
I'm guessing you're not getting a lot of response to this mostly because you pretty much won't find shit that'll handle 6-8 drives for under 200 bucks....especially so for the horizontal storage.
I know the [H] has a section of their forums devoted to firearms, so it can't be that bad. Just avoid the political forum unless you want to endure a delousing!
Then again, I'm jaded. The way I see it, you're haven't really built a system unless you've:
A) required the use of a dremel or drill press in the assembly of your computer, or
B) voided at least three warrantees in the assembly of your computer
I'd say your pretty ahead of the curve there, actually.
I've got one or two links at work for placers that sell the storage array units (supports both hard drives and opticals). most of them have a built in power supply and controller, and they connect to the main PC via USB or Firewire. IIRC the lowest price for a 4 unit I saw was 159.99. I'll post it up here.