Currently with it being on clearance, if you are specifically wanting to sell for profit I would recommend the price paid +$10 for the convenience/finders fee. Within the next 60-90 days I would recommend increasing the price another $5-$10, but definitely after 6 months I'd venture a guess that it would be over $60, and then at around 9 months to a year it would definitely be above the $100 mark.
So far it seems that the castle itself is not the draw, either. Perhaps a $20 decrease if the box has been opened, though prices (to me) are suggesting that people want the figures- you could theoretically get more for the castle and figures being separate.