Why are factory AOWs so expensive?

[masfonos]

Why are factory AOWs so expensive? 

I saw that Mossberg is coming out with their own factory AOW that will sell for $900-1000.  http://www.mossberg.com/category/series/specialty-series/compact-cruiser-aow/  Safety Harbor and Serbu AOWs were right up there around that range last time I checked to. 

It can't be that expensive for companies to use the same receiver, fire control, bolt, pistol grip, etc. but to chop down the barrel and magazine tube and weld the magazine tube lug into a different spot.  But a regular pistol grip 500 Tactical is half the price of the AOW.

A form 1 to make your own out of a regular shotgun would be $200, but AOW transfer on a form 4 is only $5.  Do they just build in the extra $195 difference into the price because they can?  I can understand another hundred or two hundred on the price because it's extra work and they won't sell as many, but I don't understand the extra $400-500.