Recently Paul Epstein et al. published a paper on the external cost of coal.

Taken form the abstract:

Accounting for the damages conservatively doubles to triples the price of electricity from coal
per kWh generated, making wind, solar, and other forms of nonfossil fuel power generation, along with investments
in efficiency and electricity conservation methods, economically competitive.

and:

Our comprehensive review finds that the best estimate for the total economically quantifiable costs, based on a conservative weighting of many of the study findings, amount to some $345.3 billion, adding close to 17.8¢/kWh of electricity generated from coal. The low estimate is $175 billion, or over 9¢/kWh, while the true monetizable costs could be as much as the upper bounds of $523.3 billion, adding close to 26.89¢/kWh. These and the more difficult to quantify externalities are borne by the general public.

Paul R. Epstein, Jonathan J. Buonocore, Kevin Eckerle, Michael Hendryx, Benjamin M. Stout III, Richard Heinberg, Richard W. Clapp, Beverly May, Nancy L. Reinhart, Melissa M. Ahern, Samir K. Doshi, and Leslie Glustrom. 2011. Full cost accounting for the life cycle of coal in “Ecological Economics Reviews.” Robert Costanza, Karin Limburg & Ida Kubiszewski, Eds. Ann. N.Y. Acad. Sci. 1219: 73–98., http://onlinelibrary.wiley.com/doi/10.1111/j.1749-6632.2010.05890.x/full

I'm sure studies of this nature are controversial. Do we know anyone who can evaluate such studies?

There is an earlier NREL report by Pamela Spath, Margret Mann and Dawn Kerr, 'Life Cycle Assessment of Coal fired Power Production', June 1999.  (NREL/TP-570-25119)

It is referenced in this new report. It's worth a read.