If the storage will need to be built out, then your argument about costs is disingenuous in the world without fossils, because those costs are currently masked by fossil generation.
Need for fossil generation backing will decline naturally as storage is built out, but will take a long time to go to zero. Pretending otherwise makes bad policy. Building storage without renewable capacity to charge it from would be stupid because charging storage by fossil fuel burning would be monumentally stupid.
You don't need as much storage if you have nuclear and you can't compare the two without accounting for (potentially weeks or months of) storage. "Building out storage" is not an unavoidable expense that just happens automatically, it's a requirement to have a reliable greed that is mostly based on non-dispatchable renewables, and thus a part of their cost.
Seeing how you outright ignore this point, I suspect you are arguing in bad faith.
Good day, sir.
It's also factually false.
* UK approving Sizewell C for £20bn https://www.ft.com/content/11ca7193-f7d8-496f-bb90-d3270b2cf...
* about 60 reactors are being constructed as we speak https://world-nuclear.org/information-library/current-and-fu...
* the US just allocated $2.5b to support the demonstration of two advanced U.S. reactors by 2028 (X-energy and TerraPower) https://www.powermag.com/updates-on-five-big-nuclear-energy-...
* just a few days ago NuScale's SMR got approved https://www.energy.gov/ne/articles/nrc-certifies-first-us-sm...