I would say around retail would be a good deal...so like $1100. It really depends on how much you love it and if the seller needs to sell or just would consider selling for the right price. Personally I could see myself paying up 50% over retail if passing on it would haunt me way more than the money could.
I think it all depends on it's condition and especially if the handles are in good shape (not dark ).
I think the most I would be willing to pay for a bag in great condition would be around $1300/1400.