Collectors items are worth what someone is prepared to pay for them. This can vary from day to day as it's competition beyween buyers that drives prices up, and this is possibly an item that may not attract that many bids.
Try looking up similar items sold on eBay (use advanced search, include completed listings) or sold anywhere else.
Armed with this information, decide what would be the lowest price you would be willing to sell it for, and use this as the starting price.
