By far and away the cheapest option is to mod a Server PSU.
Theses are all platinum eff jobs that are designed to run  24/7 under load and can be brought ridiculously cheap.


http://www.ebay.co.uk/itm/IBM-BladeCentre-PSU-2000w-P-N-24R2710-FRU-24R2711-DPS-2000BB-/262052977748?hash=item3d03931c54


there are pinouts online but you will need a soldering iron and cabling and some kind of cooling solution needs to be rigged as there are no fans on these.

I did about 10 of these exact PSU 2 years ago and they outlasted all the fancy EVGA/Seasonc 1500W PSUs we used


this one looks good too as it has 4x fans onboard

http://www.ebay.co.uk/itm/HP-373701-001-384779-001-P-Class-Blade-2000W-RPS-Power-Supply-Unit-DPS-2500AB-A-/331644387857?hash=item4d378bc211


 there uswed to be a tread over at litecoin talk  detailing this process.