I have to agree with zenmaster, prices are "about" as low as they are going to get. I was recently in the same position, my system was:
A64 3800+
2GB Corsair XMS (a recent upgrade)
A8N-SLI Deluxe
2 X 6800GT @410/1125
I got a combo from TigerD for under $400 which had a cheap MB, a nice case, an FX-60, and a nice 500W PS. Now, since I have my old 1 GB pair from before, I nearly have 2 new computers. In the combo, that FX-60 costs about $250, a price vs. performance that is hard to beat. Not to mention, the FX line is easy to OC, at least to 2.8GHz and maybe 3GHz if you are lucky. It is about equivalent to the top of the line Opty