Any engineer knows that one-offs are way easier & cheaper to design & build than production-ready designs & the factory to build them. Building a prototype car is an undergrad project. Taking it to production costs billions. You need significant volume before factories make sense, and it's not clear that SMR's will cross that threshold.
But let's say that SMR's do cross that threshold. Then what? A power plant incorporating one or more SMR's is still a mega-project with all the problems that mega-projects and especially nuclear mega-projects have. You still have all the planning & permitting costs, the large building with special design needs, the cooling infrastructure, the massive expensive turbines, et cetera. SMR's only target a very small fraction of the cost of a nuclear project. Halving 10% of the cost is not going to make nuclear competitive in a world where it has to compete with other power sources being at least an order of magnitude cheaper.
Coal plants and fission plants have a similar principle: they heat water to turn turbines. So you're highly unlikely to get their cost below that of a coal plant. A new build 600MW coal plant was estimated to cost $2B in 2008.[1]