There seem to be plenty of model 21s in 12 gauge, with 30" barrels and a pistol grip, that people think are worth in excess of 5 large.
The market doesn't seem to agree, however.
The reason for an auction is not to create bargains. It is to maximize the ratio of buyers to sellers, and create higher prices. That record high price you see for something sold at an auction should be taken with a grain of salt.
The really little guns, in really little gauge, are a market all by itself, with no basis in reality.

Best,
Ted