Hope this information helps.
The coal you will most likly be using, is from Healy Alaska, at Usibeli Coal mine, 7500 BTU per Pound.
One ton of coal is about the same heat value as 100 gallons of Diesel. 2000 lb X 7500 BTU per lb = 15,000,000 BTU per Ton / 150,000 BTU per Gallon Diesel = 100 Gallons Diesel.
The efficiency of your coal burner is a question, probalby less that the efficiency of your oil burner.
Get a price for coal in Palmer by calling a supplier.
Coal supplier may also have good ideas about coal burners and boilershttp://www.coalandheat.com/
is in Fairbanks and may have what you want.
Coal can be picked up in Healy for 65$ per ton on Saturdays.
Coal needs space, I can fit two tons in my full size pickup with 10 inch sideboards.
If you are thinking about 7500$ of oil that might be about 2000 gallons of diesel? that would be about twenty tons of coal, that's more than one large dumptruck load.
I don't belive coal is burned as efficiently as oil, so the twenty tons could become twenty five tons, or more.
I would also design in a oil system so you can go on vacation.
This link leads to a real nice boiler, that needs a stoker, probably could use a stoker from above link, http://steel.burnhamcommercial.com/products/series-4n
This link is broken, either the page no longer exists or there is some other issue like a typo.
Again I hope this information helps.