"Prices for the Model X have not been announced, but Tesla hopes to deliver the Gen 3 at a much lower cost than the Model S because it will spend much less on research and development."
At the time that you are determining prices for an innovative new product, the development costs are all sunk. They are not relevant for pricing decisions.
When determining whether to go ahead with the project, one might consider that, by innovating, the market will bear a price premium. Proceed only if the implied contribution margin for anticipated sales exceeds the development costs. Or the causality expressed above is backward; the additional R&D is lower because the anticipated price is lower.