Well, the SPS-180 power supply can still be had, although I'm not sure at what price. A call to our sales guys would clear that up right away. We still repair RD-12's and carry all parts. Since you're looking for a cheap solution, though, that may not help you.
The requirements are pretty simple ... the SPS-180 put out a bipolar 16-18 volts, plus a 5 volt logic supply and 48-volt phantom power (which you can omit if you're using all dynamic mics). I was about to include the pinout, but this forum doesn't seem to provide a way to attach or include an image; you can find it in the manual, which is available in PDF form at the audioartsengineering.com web site.
Give our support people a call if you need help with the beast: 252 638 7000.
Scott