This might be of interest to {re,}sellers of backend-specific mythtv boxes as well.
A while back I'd been considering going RAID 5 for the mythbox. That ended up seeming like a bit of overkill for my usage. However, I did go ahead and go raid-5 for my primary server.
For portability reasons, I wanted a non-card-based hardware solution, and though the prices out there from resellers/builders were pretty high, stumbled upon the fact that Areca's ARC-5010 IDE to IDE device could be purchased standalone:
http://www.areca.us/IDEIDE.htm
Even better, at the time still had online ordering up on their site, though not linked from the main page (probably due to complaints from their resellers...thank you, google!). Directly from them, price for primary unit was ~$600 give or take ~$50, IIRC. Takes up 3x5.25" space.
Even better, the optional LCD/Button interface (not shown) was <$40. Takes up 1x5.25" space.
They do have a prices/inquiries button on their where to buy page, and I know they sell in 1 unit quantities (shipped from Taiwan, even), so such prices may still be available from them directly.
Attempting to buy the unit elsewhere will get you a markup of $250 or more, esp. once the resellers add an enclosure and a firewire to IDE bridge board...then they're selling for ~$1200-$1400!
And yes, it takes >128GB PATA drives.
-brendan