I bought an iMac marked non-functioning from Goodwill. When I saw the specs on the bottom of the stand, I knew it had to be an Intel model. I grabbed it for $25 and took it home.
As soon as I got my $25 iMac home, I plugged it in and found no signs of life. I popped it open and tested the power supply with a voltmeter; it was putting out nothing. I ordered the new power supply, popped it in, and my iMac was as good as new!
Make sure you use a magnetized driver to remove the screws holding the screen — they're easy to drop into the iMac. Also, the EMI shield is a total pain. Other than that everything is pretty easy.