It is not just the base capital cost. You also need to hire the expertise to run it. And that can easily run into the billions per year. And most of that talent is foreign and the current Administration is generally against immigration (though maybe Apple could get them all those Trump Gold Visas. 😛 ).
And of course you can't build a fab in a day. And I expect the equipment that goes into it has long lead-times. And once you have that fab, it is designed around a certain process and capacity. If what you need changes, then at best you spend billions making changes and at worse you spend tens of billions starting over.
Better for Apple to do what they are doing now, investing in existing Intel and TSMC fabs based in the US and helping them fund new US-based fabs on newer processes (I don't see TSMC ever letting their absolute latest processes leave Taiwan). That way, you have first-access to the product. This is what Apple did with TSMC in Taiwan to help them scale to the levels they are now.