What is the value of a Smith and Wesson Model 2 revolver used during Civil War?

You will need to provide a solid, undisputable provenance as to the Civil War use. If you can, it adds quite a bit to the price. You will need to seek the services of a professional. I would recommend Supica and Nahas. Value can range from 200-7000 USD depending on condition, variation, accessories. That would be before the Civil War connection.