I too had been searching for a fast and cheap RAID system for the last couple weeks. I do mostly After Effects motion graphics and also needed uncompressed HD capturing direct from my camera via my Blackmagic Intensity card. Found several thorough reviews on AMUG – Arizona Mac Users Group. They led me to getting DAT Optics Q-box-M 4 disk raid enclosure and a highpoint 2314 card. I stuffed it with 4 reconditioned 500MB Seagate ST3500320NS-R (Enterprise Series). I assembled it last night in about 10 minutes, and if my Blackmagic Tests are correct, I’m pulling 400MB/s read and 370 MB/s write!
This is in RAID-0 mind you (non-reduntant, i.e. fast but not safe), but at that speed I can probably go RAID-5 and still get the 220MB/s needed for capture. Best of all, under $600 total.