I would check out what they have gone for on eBay.I have the $1.00 one and it sells for anywhere between $8.00 to $15.00.Average it out.I would suggest just pricing it to be fair because there will be plenty of them at the convention I would assume and you do want to get rid of it right?
I have been selling at antique shows for over 25 years and this is like any other show....price it right and it will go.Price it too high and you will be taking it home.