Nuclear reactors are expensive because we don’t build any of them.
Solar and wind occupy way more land for the same power production and can’t produce baseload power without battery storage systems that cost 5x as much.
Nuclear reactors are expensive mostly because the regulatory requirements make them expensive. There is a lot of room for advanced nuclear (e.g. gen III reactors) that can address a lot of the problems and bring down the costs. Unfortunately, we don't have a clear regulatory pathway here yet, but there is some progress being made recently.
Solar and wind occupy way more land for the same power production and can’t produce baseload power without battery storage systems that cost 5x as much.