Based on condition, I'd say $300-400. These and similar games pop up on ebay often, and while asking price on Ebay is always higher, they don't seem to move until relisted with a best offer price....

What kind of metal is that in the target area? I'd try starting with a windex type cleaner, and it you need to work harder, maybe some mean green. You could prolly use a 'softer' scotch brite pad or bristle brush on the metal target area to brighten it up. It does not appear to have a large amounts of wear you sometimes see on these games from the little balls the gun shoots.

have you still got this target skill game