Initially, there was no savings in buying the kit because that is the only way they came.
I think we are missing the point here. This was around 1975. If you were a collector then and wanted to own the Madison cars the only way to do it was to (1) find them and (2) pay the price. They were rare (relatively) and expensive. Then there was the 'condition' issue. That made them more expensive. Williams produced this virtually identical set (except for rivet count) made out of the same material for not much money. It was the only way some collectors and operators were ever going to own the 'Madison' cars.