If you are thinking of selling them I'd make a list / spreadsheet and put a search into Ebay under 'completed listings' and see what they are worth, as with most things, some will be worth less than nothing and some possibly a great deal. If any aren't turning up then put a more general google search in and see if anyone else is selling the same thing, so you can at least thin out your value to knowledge base and then research more extensively any you can't find which by the laws of average are likely to be the rarer ones. x