It's the most expensive if you don't already have the infrastructure & experience needed to support it. Of course in places where nuclear is barely used or not used at all, it's going to be more expensive than others. But the US doesn't have such a problem – in large part due to lifetime extensions (which allow plants to operate for another 20-40 years, up to a maximum of 80 years), which bring nuclear's cost down to comparable to renewables. Without lifetime extensions though, nuclear indeed would be more expensive than renewable energy.
Renewable energy also gets subsidized significantly more than any other form of energy – in the US, solar and wind both get roughly about 16x the $/MWh of nuclear, and 2x the total amount of budget. The EU also puts like half of its total energy subsidies into renewables (and a third into fossil fuels) and almost none in to nuclear. That should probably be taken into account too.