Fabs are very expensive. You can see numbers ranging from 4 to 10 billion dollars each. Those are the fixed costs that you now need to spread over production.

Fabs are very expensive. You can see numbers ranging from 4 to 10 billion dollars each. Those are the fixed costs that you now need to spread over production. It looks like Nvidia does around 20 million chips a year. If a $4bn fab was useful for 4 years, then those fixed costs work out at $50 per chip! If you make other people's chips on the same fab then the per chip costs go down, assuming there is spare capacity. The economies of scale really do help. Which is why there are a few foundries who do most of the chips, and those foundries can spread the costs over a large number of chips including later ones that don't need the newest process. For example Intel is known to do their CPUs on the current process, while doing the chipsets on the older processes. In other words, work out what set of numbers would make sense, and you won't be able to find any. New processes keep getting more expensive, and competitors adopt them too, so you have to sustain your current fab as well as the work to do the next generation one. This requires a lot of available money. Don't build a fab unless you are sure you can use almost all its capacity for the next several years.