Hmm it seems that there are not many decent RAID cards around for that price with 4+ ports. There is one that keeps popping up but it is competitor branded so I cant really point you to it. Personally I would much rather get another motherboard and keep the RAID card you have currently since it will cost about the same, and the RAID card isnt of a great brand lets say. But you could probably find it through google, it is rated as 4 stars, costs just under £30, and as I say, is of a competitor brand. the brand name has .com on the end, its easy to spot.
Have you thought about maybe just getting another 2 port RAID card so you have 2 RAID cards installed? Or do you not have enough PCI slots on your motherboard for that?