Hm. I was kinda thinking the $50 ballpark.
Looks like Newegg has a HighPoint RocketRAID 1640 for $50, but it's vague as to whether that's hardware.
The 1720, which is $75, is supposedly "hardware-accelerated".
Anyway, I remembered... these SATA cards wouldn't use the on-board BIOS's LBA, they'd use their own BIOS, so the card would be fine with 48-bit LBA.
You are *not* going to find a full hardware-based RAID card for $50. I'm actually surprised there's (possibly) one for $75; IIRC the last time I looked they were all over $200.
I would double-check driver support for your specific distro before considering the 1720, as I see it is based on a Marvell chipset (Marvell is *not* particularly good about releasing hardware specs to the Open Source community). Also note that the 1640 is based on the (now obsolete twice over) SATA-I standard, and the 1720 has only 2 ports... not good.
For your budget, your best bet is probably something like this
. Cheap, SATA-II (so only one gen out of date instead of two), 4 ports, and a Silicon Image chipset with mature Linux driver support. Just don't try to run a software RAID-5 array on it and the performance won't totally suck.
(And quite frankly, your best bet really is to upgrade the whole server instead of trying to nurse that ancient box along for another few years.)