If you are only going to mine on these machines, the RAM you are specing out is overkill, IMO.  I have only 2 GB in my mining rigs and they are fine.

I went the AMD route, personally, and built something close to this:

ASRock 970 Extreme 4 - $100
AMD Sempron (cheapest - forget the model) - $40
RAM - 2 gigs cheap ($10, maybe $15)
Cheapest SATA HD I could find

I bought 1200 watt PSUs, but i THINK you will be fine with the 1050.
Cheapest 7970s I could but at the time

Good luck!