>> The unit price of the cars isn't really relevant to the cost of developing it's software. A low cost model that moves sells a lot of units, can likely afford to spend more on software compared to a high cost model that moves only a few units.

You didn't? Of course software costs are part of the unit costs for each car produced, just how those development costs are actually allocated is up to Finance (accounting and controlling) to decide. And of course those costs are relevant, as all the other costs of a car maker.