About 10 years ago early Model 21 gun with DTs and old style "canoe paddle-style" butt stock in very good original shape would sell in $2500 to $3000 range. Not sure what gun like that would bring today. Honestly I have not seen prices for typical pre-Custom shop era SST field grade guns move for a lot more cash in last 10 years. Dealers are asking a bit more, but the guns seem to linger on their web sites w/o being sold.
This is one of the competitors with London address.....
This is just one example with many more out there. The competition for buyers is very, very fierce.