And by that same logic a 100ft canting keel maxi should be double the cost of a 50 canting keel racer of the same standard...Anyone here know the cost of each of the above??

The reality is that there are a lot of factors involved in costing a boat for proper production (not just knocking out a couple of boats in the backyard).

essentially boats in the 16 - 18 ft range should be close in prod cost, a 20 will cost more as the loads are higher and the parts bill is larger due to the up sized parts required etc.

But I think there is demand for a well priced 20 that is modern and not too complex.