[kevincox]

Money is fungible so it is really hard to say but it is entirely possible that the base model doesn't pay anything for the seats. They could sell the car with $10,000 and expect that 1/2 of the customers pay $500 for the upgrade. Those customers are essentially paying to install the seat hardware in all cars (because it is cheaper than them paying for a new production line that makes 1/2 the number of cars). So in 2 the purchaser of that car still pays $10k and their "other half" who statistically bought the heated seats paid for the $100 cost in their car.

You can also picture this as a marketing cost. Maybe Tesla things that a $100/car marketing cost is worth paying because they expect that 1/2 of the cars will pay $500 so they have $150 expected return.