I bought 2 gigs of DDR2 ram for moms pc for 18 bucks x 8= 144 bucks.
1 TB drives are going for 90 bucks on newegg.com
Now if your thinking Intel i7 with DDR3 memory and board now your talking big bucks!
The Mac Pros don't use the Nehalem i7 Intel "Bloomfield" quad core processors which were released five months ago... they use two of the Intel Nehalem Xeon Quad core "Gainestown" processors (which won't be released to the other manufacturers for another couple of weeks). Retailing for around $2500 each, the Gainestown processors run about $2,000 more expensive than the i7s with the same clock speed which can be purchased for around $550 each.
You also have to use ECC memory... which the i7s don't support.
Life on the bleeding edge : )