In American doubles, what someone paid for a 12-gauge has virtually no bearing on the price of a similar gun in 20-gauge! I was in a shop a few weeks ago that had two Model 21s for sale. Both were pre-war and the 12-gauge for $3600 had a slim forearm while the 20-gauge for $8600 had a beavertail. Both had single selective triggers and ejectors.

Here is one with no case on gunsinternational in the 1936-style -- http://www.gunsinternational.com/detail.cfm?id=100039260&string=cid=149

This looks like the best NID deal this week -- http://www.gunsinternational.com/detail.cfm?id=100049928&string=cid=149