Based on the -limited- sold and completed eBay listings I've seen of similar style knives, I would say at least $200-300. All were in better shape than yours, but yours was dug at a known site, which more positively associates it with civil war use, perhaps adding value in lieu of the damage. I did see a csa dagger that was very complete in great condition sell for over $1,300, so that would give you the highest possible end, tho unlikely that high.