i'm not sure how far irvine is from LA, but i found this ad, which seems like a great deal. He's selling the whole computer which includes a 4800+, 4GB DDR memory, 7800GTX, and a lot of other stuff but w/o the HDD for $95.. sooo.. he may even part out and sell the cpu to you by itself. He didn't mention anything about the case or powersupply, but it may be a good one...
You can put in an offer for like $35 for the cpu... but i would also try to get the video card and the extra memory... go check it out!
Computer for sale, state of the art at the time when built!