It is highly unlikely for a premium to be attached to an used Model S. First, there's the premium. Then there's the federal tax credit. Then, in case of Washington State, there's a sales tax that wouldn't have been there had it been new.
At least here in WA, there will not be a premium and if anything, a serious amount of depreciation. Just my two cents. And don't take too much consideration into eBay bidding info, those things are not really binding so technically I can go bid a million bucks and just not follow through with the transaction.