Getting screwed over on a payment for a parts purchase?

I'm not totally familiar with current ebay policies, but once upon a time if a seller offered to sell something to you outside of eBay, it was a violation.
I might report him to eBay if I was you. You may not get your money back, but it could help others and it may cause him enough financial impact that he thinks twice..
Hell, he may even suddenly "find" the money.

Hope it works out for you.