I'm getting the numbers from the '2012 standard Catalog of firearms' 22nd edition, page 821. My apologies I added an extra 0. It says a DH in very good condition is worth $6,000 and for a .410 add 500%. That would be $30,000 not $300,000. It states that there were only 280 DH models were made with single triggers and only about 280 ventilated ribs were manufactured. It does not say how much should be added for a single trigger of a ventilated rib. Sorry for the confusion.
Here is the Auction house website:
www.thecobbs.com
this is the listing:
http://www.auctionzip.com/listing/1282484.html