It's not "da costs", it's actually really, really really expensive to build new nuclear reactors. Most of that comes from increased labor costs, which in turn have ballooned largely due to increased regulation and oversight requirements, which I would argue is not something we should do away with.

I wouldn't necessarily mind having a reactor or two acting as base generators especially during the winter, but

1. In Germany we've been searching for a secure waste site since the first reactor went online in 1957. If we haven't found it yet, we never will.
2. There's not really a reason to hope for cost reduction of reactor construction once we do it at scale, because requirements and local acceptance are too heterogeneous to implement any sort of scaling construction. Every jurisdiction will have its own risk assessment and usually the locals are none too happy about a reactor close to them. I just don't see something happening in that regard. Wind turbines and solar panels on the other hand can be churned out in factories at scale, which is why they're so cheap, comparatively.
3. Therefore, personally I'd rather invest in green H2 as an energy storage solution. We can easily generate an enormous electricity surplus during the summer months, but lack long-term storage of the electricity. So we shut off solar and wind farms when they're over producing. Wouldn't it be neat to instead let them keep generating and use that surplus energy to power power-to-gas plants E. G. with H2? It's an enormously power-hungry process, but if you do it when power is basically free...

Oh wait, we're already doing that and it's already cost-effective. Now, if we were to take that process and build it at scale... for example by not spending 12-20 Bn 💶 to build another Flamanville, Olkiluoto or Hinkley Point C... I think that might actually work.