Late-2006 iMac doesn't power on; Bad PSU suspected

Forgive me if this topic has already been posted but I've search high and low for a similar situation.

On Friday night, I placed my iMac 24-inch into Sleep mode and on Saturday when I tried bringing it back up, the computer just shut down. It's like totally dead. I know it was still in Sleep mode on Saturday morning when I interacted with it because of the pulsating sleep light in the lower right corner.

So, seeing as how I've experienced a similar situation with my PC, I believe the iMac has a bad Power Supply Unit (PSU) that needs to be replaced.

First, looking at the DIY manuals, I couldn't find one at all for my model to replace the PSU. Does one exist?

I'm not at all looking forward to taking this to the Apple Store for evaluation then exorbitant price estimate (may as well get a new computer and chunk this one if the repair is over $300.) I would like to try replacing the PSU first myself.

By the way, has anyone ever had this PSU replaced in their iMac by the Apple Store and how much did you pay?

Thanks in advance.