I have a bottle of Martell Cordon Bleu Cognac Reserve CU2503 bought about1980. What is it worth?

Your bottle is worth a few hundred without question as long as it's not opened, And the label is still intact, If you really want to sell it put it on e-bay, or try and sell it on your own....|||Your bottle is worth 139.99 retail in TN. No liquor ages after bottling. Therefore the time you bought it has no effect on its value.