> A major reason nuclear plants are super expensive is because we do it so rarely

Once you have your supply chain running, and PM/labour experience, things can run fairly quickly. In the 1980s and '90s Japan was starting a new nuclear plant every 1-2 years, and finishing them in 5:

* https://en.wikipedia.org/wiki/List_of_commercial_nuclear_rea...

France built 40 in a decade:

* https://worksinprogress.co/issue/liberte-egalite-radioactivi...

More recently, Vogtle Unit 3 was expensive AF, but Unit 4 cost 30% less (though still not cheap).