I'd say late 1880s, and the value is very subjective. I know a prominent dealer who would charge $1,500 or so for this piece. Perhaps closer to $2,000 if it was clean with no staining or other flaws. But he would be sitting on it for months (if not years) and you'd see it on a recurring basis at the National.
As it is in this condition, I would say $600 - $800 in Hunts, REA or Heritage. Maybe $500 - $600 on ebay. A lot depends on how it's sold, and the commission that a seller is willing to pay. As someone who collects this type of thing, I personally would pay around $600 (or maybe $800 if the stains could be diminished/removed).
Hope this helps... cool piece
