I would do the very opposite of what L Gebhard says - offer him less. In fact offer him $350 and let him talk you up to $500. If you're in the right place at the right time (which it sounds like you are) and if the seller has no interest in trying his hand at ebay than it is most certainly a buyer's market. In fact, the seller is very lucky he found you because the scrap yard wouldn't give him more than $25 for this setup.