Are cheaper variants of a model more expensive to produce?

[Futuramic]

I was thinking about the economics of manufacture and came to the conclusion that it might be cheaper, per unit, to produce the more expensive variant of a car. However is this true? I was only thinking about the normal models in a range, rather than any super stuff.

Starting from scratch I have decided to produce a range of a rear wheel drive four door saloons with reasonable performance. One such exists in the real world and it should be obvious but this is only a hypothesis.

Logically I would have to start with the top model first, as it would have the highest requirements for the body shell. I decide to fit a straight six engine coupled to a six speed manual gearbox. I go off and design the engine to produce 350 horsepower reliably and submit it for emissions and fuel consumption testing. The homologation certificates come back so it is deemed roadworthy. I go on to manufacture a gearbox capable of withstanding its torque and build the rest of the drivetrain into the body shell. In turn that goes off for crash testing and all the required shakedowns before mass production. I start here as I know that the various components all have to withstand the power produced and the handling has to be up to scratch.

I go on to consider a base model variant. This uses the same architecture however will be powered by a four cylinder and has a five speed box. I already have a body shell, but this will require modification to fit the smaller engine. The bare body, once done, shouldn't cost any more than the six cylinder car. It uses the same amount of metal but there are differences under the bonnet. The smaller engine upsets the handling balance so this has to be re-assessed, new suspension designed and further testing done. I also have to design a new gear box with different ratios to cope with the revvier but less powerful nature of the small engine.

Having already developed the fast variant there will be considerable costs involved in adapting it to become the base model. I know that the components of the slow car will be slightly cheaper, in that the engine might used cast internals over forged, and will be smaller but does the cost of designing and perfecting all of those outstrip the savings? Of course the counter argument is that the cheaper car will cater to a different audience thus improving my overall sales, but I don't know whether it would be worthwhile. After all I would have to consider two production lines and have separate tooling for each variant.

There could be cost savings in component sharing, there are certain "upgraded" parts from the fast car that could be swapped on to the small one. But again these would be minimal. The brakes would have to be re-designed as the weights would differ. Similarly final drive ratios would be different. Basic stuff like drive shafts and differential casings could remain the same, however.

I haven't gone into interiors, optional equipment and spangly bits as I was merely thinking about the mechanical side of things.