Just a headsup, the CX500 on sale at newegg for $50 + $20 rebate. http://www.newegg.com/Product/Product.aspx?Item=N82E16817139027 I have 1 on an oc'd ant and it works great. If you can find a way to turn in multiple rebates, then you can get a bunch of these at $30 each. Would only cost $150 to power 1TH/s.
You know cheapest option is dell 750 2850 poweredge. You can run 2 s1 not oc on this or overclocked and it will cost you no more than 12gbp