Regulations don’t change the cost that much. Yes, you can save money by not having a containment vessel around your nuclear reactor but that’s a major risk which has inherent costs. On net it’s cheaper to have that containment than not irregardless of regulations.

Dig into the rising costs, and you find root causes like 3 mile island showing the industry it needed to increase maintenance spending. It wasn’t some arbitrary overreaction but simply the damage accumulated enough to cost a billion+ dollar asset. Thus much of that “increased” spending is simply asset preservation.