What I did was put a wanted ad in Craigslist. Ended up with about 15 supplies for $15. Watch out for Dell supplies. I didn't have much luck with those. I'm sure there is a way to make them work, but due to time constraints, I just used ATX supplies. There are lots of people out there with power supplies just laying around in boxes.
This is the power supply pulled from a Dell Optiplex GX280 Desktop, not tower. It will fit into a similar GX270. They are used but functioning perfectly. I have 4 total, they are $10.00 each. If you want all four, we can make a deal.
The connectors are as follows, 20 pin ATX, 4 Pin 12V ATX, IDE Power, Floppy Power, and a SATA power connector.