RE:RE:NG BluesHuntingman your costs are correct for coal and NG, but your missing some details, firstly although direct cost of coal is $2.1 per tonne, delivery is actually $1.15 approx. so that makes cost of coal $3.25 approx. whenever the cost difference is within $1 range between the two, NG is the fuel of choice as it burns cleaner and more effieciently.
Just an FYI
GL