Are you guys sure you're looking at ECC Registered PC2100 DDR? I went to pricegrabbers and entered "ECC registered DDR" and Kingston did not come back as one of the manufacturers. No cheap deals from Viking, Corsair, Crucial either (well, 2x256MB for $108 *is* damned cheap when you think of it!)
Anyway, I then searched for "ECC DDR" and a bunch of cheaper options came up, including Kingston and Crucial DIMMS.
But ... this board requires ECC Registered DDR. Not sure what it will do if you put in non-ECC registered DDR but I do know what will happen if you put in non-registered DDR ...