The best way to determine true value of your cards is to price what they are going for on eBay. Sign up for an account, and search by Completed Auctions.
You will need to keep in mind that the quality of the cards is EXTREMELY important. One crease can devalue a card more than 70%.
Also, the cards have different values depending on the time of year. If you are going to sell cards, then in April/May is the best time.
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