Shouldn't be too difficult to work it out. From my experience in a slightly different modelling company (Britains/First Gear) the costs of producing basic, uncomplicated, undecorated (largely) base units was vastly outweighed by body mouldings. Not only are they of much greater complexity, often requiring 'slot-in' alternatives for different classes, periods, etc., but also they require much more input in the R&D side, and in the mould forming itself. Simples!