Since you state that the 2nd bidder really wants the frame, I am assuming that you have been exchanging e-mails with him? If that's the case, give the originaly bidder a hard deadline for completing the transaction. If he doesn't pay by that date, tell him it's cancelled. You ought to be denote that the winning bidder failed to pay on eBay and avoid your final sale fees on there. Then simply sell it to the other dude on the side and save yourself quite a bit on eBay fees. Are you able to accept credit card payments? For bigger purchases it's a bit of a hassle with just a standard PayPal account that cannot take credit cards...

p.s. here's the official eBay "what if a buyer doesn't pay" answers.
http://pages.ebay.com/help/tp/unpaid-item-process.html
http://pages.ebay.com/help/tp/questions/nonpaying-buyer.html