Well all I can say is, that if he only wants to spend $300 on a RAID controller, he better already have the drives, or it could come as a shock!
I bought my HP NetRAID-1 for $299 (inc tax) brand new, though it was in a clearance, reduced from the original $700-odd from when it was released.
If he's not really heavily into image/video editing or similar, DVD ripping, anything extremely data intensive - you may want to point him towards IDE RAID - unless the reason he's looking at SCSI is because he already has the disks.
For one thing IDE disks are dirt cheap, and there are many equally inexpensive controllers around...
One thing that is almost pointless mentioning, but worth it because its not funny if it happens; SCSI RAID controlelrs tend to be full-length PCI cards.
Quite a few systems simply dont have the case space or mainboard clearance to install a full-length card.
Also, because they have a 'CPU' on them, which gets rather warm, cooling nuts (like me) tend to add HSF assemblies to the card - which makes PCI card retention slits an absolute necessity...
Good Luck!