It is always difficult to make comparisons between the cost of heating with different fuels, given that there are a number of different suppliers in the market, different electricity tariffs for day and night time and different costs according to the quantity purchased and distance (particularly for solid fuels such as logs and coal).
In today’s market, wood pellets, woodchip and logs are generally a cheaper way to heat than electricity and LPG and in many instances, oil. Mains gas is the cheapest way to heat where it is available.

Further details are available here