Closer to $40b for a new fab for an established company to do it all correctly. It's a much more major investment to open a fab without ever doing it before, then continually use the brain power/institutional knowledge you've built up to stay near the forefront of fab tech, and then basically have weird incentives to build a foundry for only your products rather than the world at large.

You're setting yourself up for making a huge part of your future revenue stream being set aside for ongoing chipfab capex and research engineering. And that's a huge gamble, since getting this all setup is not guaranteed to succeed.

If it were only 20B then Apple would jump at the chance.

As would almost innumerable others.

Apple has around $55B in cash, much more in stocks.