Hardware RAID options on Xserve?

We're building a new web hosting server and are considering purchasing a Xserve. I couldn't find any info on the Apple site, but is hardware RAID an option? If not from Apple, could we add a Sonnet ATA card or alike, to give us RAID level 1 on two of the drives? What are the disadvantages to doing this? We currently run an OS X 10.2 Server on an older G4 for file server purposes, and find that software RAID on 2 pairs of mirrored drives really puts a load on the CPU. Plus I have read that if one of the drives dies, we cannot just put another in and rebuild. Our budget is $3500US, so an Xserve RAID is not really an option. We're also considering an IBM xSeries 345 and Dell PowerEdge 2650, both running linux.