I'd stay away from going the absolutely cheap route. There's so much junk on Ebay right now you never know what you're getting. There are deals to be found, but like my dad says, do it once, do it right. Nothings sucks more than a leak especially when there's little or no room to fix it once the motor is in the car. Scoggin-Dickney has some good deals right now. A stock replacement from Milodon is something like $80.
http://www.sdpc2000.com/default.htm