In my mind, the K22 is perhaps the best 22 revolver ever made. Looks like a circa 1953 gun, if I eyeballed the serial number on the tag correctly. $400 would be a great price. $350 even better. But I would think he will want more.
I picked up a K 22 last year that dates from about 1955, in similar condition, but still a great shooter. Dealer at the gun show had it tagged $475 but I traded another S& for it that I was into for $300. It's hard to find any K22 for less than $400 these days and I've seen some pretty sorry looking specimens still sell for over $300 at auctions. Hopefully you can play up the finish defects to bargain him down some. Good luck!