To make anything on a 16GB model on eBay, you would have to sell it for $850 just to make $50. 13% fee between ebay and PayPal plus shipping costs.
649 + tax= 685 or so
850 - 13%= 740
740- $10 shipping =$730
Not much profit, so availability would have to be really tight to get prices over $900 and you take a huge gamble if they come back in stock quickly.