If you go down to basic physical material costs, Surface area of car, Metal cost, Glass cost etc, are the things which will determine car price in long run, So car which is weighting let's say 25% percent less can be be built cheaper compared to car weighting more. Less doors, less glass use, less paint, less material, less battery needed for same amount of distance, which brings down to cost.
Ok, lets think of it other way, all things equal, if you are tasked with cutting costs of vehicle without cutting back things which makes your brand unique, and without reducing margin or running on loss how will you do it?
You make vehicle simpler, with less expensive parts. That's how hardware design works.
Cutting back on quality or software expense is not a option for Tesla as that will make Tesla equal to any other Chinese EV brand.
Raw material is less than half of the price of a vehicle, right? Assuming it’s 50%, a 25% smaller car would save 12.5%.
I would be surprised if raw material is even 50% of the cost.