The Cube PSU as a service part goes for almost $200 - but you don't need to buy it! And you don't need to scavenge on eBay for one either. If you are in need of a new or spare PSU, you need only purchase a Dr. Bott DVIator, which includes the identical power supply that shipped with your Cube. And I do mean identical in ever way (little white Apple logo included).
See it leaning against the B&W tower on the right?
For under $100 you get the PSU you need and you can toss or sell the display adapter part :)
