Do you know if it is a one-pipe or two-pipe steam system? If it is two-pipe, he may wish to convert it to hot water heat and keep the existing radiators, and probably gain a fair chunk of efficiency from the deal. Many of the old one-pipe systems didn't work nearly as well going from the hand-fed coal to the intermittent firing of oil without a huge loss in system efficiency.http://www.heatinghelp.com
is a great resource for just this sort of topic.
Axeman-Anderson, EFM, and Keystoker all make coal boilers that can run as hot water or steam.
I lived in a late teens/early 20's home on Long Island, NY with the original coal hand-fed boiler converted to oil. I don't recall what we were paying for oil, but it was the mid/late 80's. I'm sure well under a buck a gallon. Most of the loss of efficiency is having to heat up all that iron and water each cycle to the boiling point just to get steam to rise into the radiators. It did, however, work well and I loved having the steam radiators.
I bet with a coal stoker boiler, the idle fire would keep the water at a low 'simmer' and make for quick steaming when the t-stat calls for heat. It would be 'fun' to build a modern home but style it in the Victorian style and install a 'modern' steam system with coal. You can still get iron radiators new.......