hmmm, if he didnt close out the listing, then I think technically he probably is obligated to provide you the goods at the auction price. However, he'll likely fight it since it means prolly he will have to buy a new one and then sell it for half price.
The question is, do you want to fight him all the way down the line for this? Cuz i'm pretty sure he'll go as many rounds as he can. You'll have to get ebay and paypal involved, open a dispute (after first trying to call him - paypal requires that), then wait up to four weeks for the resolution to work its way through paypal. And at the end of which you'll also have one pissed off seller who may well literally piss on the keyboard before mailing it to you.
Still, it might be worth just checking with paypal and making the initial phone call to him letting him know you're disputing it, as required, even if you decide to drop it later.