Specialised ribless woodcock OUs are made by several makers like Franchi, Verney Carron and others. They are short barreled and that probably keeps them from becoming popular in the US.

As for the expense. Some makers seem to charge more for what they do not install. The pics show a rounded end on the monobloc rib section and a ramp on the muzzle. How that coudl cost more than a full laid top rib is a puzzle.