Buy.com has the CoolMax 500W 120MM ATX Power Supply w/ Silent Fan for $28 - $28 rebate = FREE w/ free shipping.
Wow I would definitely buy one of those if I needed to kill my teacher. I'd just put it in his computer and wait for it to blow up!
Lol, yes, be careful to ALWAYS buy GOOD quality power supplies. It may be tempting to go cheap, but *ahemmmm* personal experience...don't ever do it