It's only worth as much as a person will pay for a used camera. Try advertising it on Ebay. You can get a good idea from their website, as how much you can expect to get.
I checked eBay. There are several different kinds of Polaroid Pronto's listed. None of them have bids, even with opening bids of $4.99 offered.
Think about putting it in a yard sale, but don't feel too bad if it is just junque. I'm sure that it gave someone many happy moments and it has served its purpose.
news papper ad or a pond shop!!! or maybe on here if you ask around someone might need one ,put the price and how long you hade it and a number to call back or email