It depends on many things. Who wrote it, is it hand written or printed, condition of the piece. Various other things. You'd need to find a specialty dealer for it.
It depends on the era and type of music. Vintage sheet music can range from just a few cents on ebay to 100 dollars a piece. It would be difficult to sell them individually if you dont have the time but also selling them in bulk will not allow you to make the most out of them.
