The cost consists of a number of factors: materials and labor, design issues, and legal challenges. A global effort to build up proper nuclear infrastructure means the design issues will be far less of an issue: just design one really good reactor, and build a few hundred. And governments can (and in the case of China, will) move to limit the possibility of legal challenges. That just leaves materials and labor, which are comparable to similarly-sized industrial structures: considerable, but certainly not insurmountable.
