I suggest you research recently sold similar items (Ebay and elsewhere) and decide what price you are prepared to pay. No one can really answer this for you as everyone's threshold is different, it depends how much you want the item now, how difficult it may be to obtain from your local store, and some would pay more or less for the same item in the same condition.
Assuming that it's been authenticated, these are hard for many to obtain and resellers can command a premium. Retail on this bag in the US is $11,900 plus tax, so call it $13K. Getting close to retail on either side is realistic - how much above retail including tax it's worth is a personal call - and frankly if well below retail I would worry about a scam. Please take care and protect yourself as a buyer