Agreed, you want PCI-e (PCI Express) and not PCI-X.
Hexus recently revieved the HighPoint RocketRAID 2300 which costs under £90:
http://www.hexus.net/content/item.php?item=9556
Also, Scan frequently have the XFX Revo 64 3-port PCI card for just over a tenner. Hexus also reviewed that a while ago:
http://www.hexus.net/content/item.php?item=1366
I have one of the latter and am very happy with it. Because it's PCI it's not as fast in day-to-day use as some RAID solutions, and is possibly a bit slower than a standard SATA drive at small reads & writes, but it DOES give you the redundancy of RAID 3 for just over ten quid. I certainly don't notice it being any slower than when I just had a single SATA drive and in any case you want it for the redundancy rather than the speed. For that price you could even buy two if you're worried about what happens if your card fails!
Regards