While the smallbore premium for vintage guns is more generally true, there is also a smallbore premium for some new guns. Check out prices from Lion Country Supply on their Ugartecheas. And not only doubles: there's a premium for the Benelli Ultra Light 28ga.

If we're talking doubles for upland hunting and classic guns, of both American and foreign origin, in order to get guns in the same weight class as a British game gun in 12ga (or some continental game guns), you need to go to a 16 or 20 in an American classic.