The gun in the pics has better wood than similar Model 21 guns of that particular time. If all original as it appears to be I would want at least $3500 and closer to $4000 the better. I don't know what the future brings for guns like this. I remember in early 90s they were asking about $2500 yo $3000 for 3" Duck guns in very good original condition. At some point in time they doubled or almost doubled in value and don't seem to be appreciating much more. It is a tough sell now because there are mounds of very good doubles coming to market now and that isn't going to change for near future.
Sadly even though such gun can last grandchildren's lifetime if given some care the way things are going those poor kids will be living in "forests of polymer plastic".