That cost is a property of the regulatory environment, it isn't intrinsic.

You can buy a floating nuclear power plant in the form of an aircraft carrier for a lot less than $16B. The US Navy builds these things as a matter of course in a few years using standard designs they crank out by the dozens.

Those carriers have 700MW thermal output reactors. The new generation EPRs built now are about 6x that.

And yes, carriers have a lot less rules because it those have issues we're already in big trouble. You'll need strict rules given the big impact a failure has. No one has an aircraft carrier or sub in their backyard (not constantly that is)

Standardizing a design and building N of them would help though