Here is what I am using to power my gs. I only have 5 now but hope to get quite a bit more later on.

http://www.ebay.com/itm/HP-Proliant-DL580-G5-1200W-12V-AC-Hot-Plug-Power-Supply-438202-001-441830-001-/301142899605?pt=US_Server_Power_Supplies&hash=item461d83fb95

its a 900w ps when run at 120v. or 1200w at 240v.

So at 900w at each one runnng at 7 w

900/7= 128 gridseeds on one HP power supply

or is some brave soul is brave enough, he/she could plug in 240 into this powersupply

1200/7= 171 gridseeds off one power supply.

all for $28 I was able to get mine for $17 a couple of months ago.