I’m no expert but I’d recommend scouring the second hand market and see what a comparable bag would go for. By comparable, I mean age of bag, condition, and style. You could also ask for price quotes from different resales but keep in mind they lowball you since they take half (if not more) of the profits. If you are selling it yourself you can theoretically double their quote and you’d get an idea of how much you could make if you sold it yourself.