From the Congressional Research Service, in a report on the cost of new EPA regulations that will shut down some of the worst polluting coal plants in the country:
The costs of the rules may be large, but, in most cases, the benefits are larger.
The full report is here. Brad Plumer has the user-friendly summary here. Bottom line: The cost of the new EPA regs is almost certainly being hugely overestimated by the power industry (surprise!), and the benefits in public health will almost certainly be far greater than the price tag for replacing our most antiquated coal plants — which are mostly near the end of their life anyway — by more efficient combined cycle natural gas plants.