I don't believe our electric rates here will go up in the foreseeable future. LP can fluctuate a lot as we saw last winter with near $6/gallon prices for a while.
NG while cheap is only available in towns.I would look into an off-peak electric system with an LP forced air back-up system. The forced air is nice for quick recovery after the doors get opened during the cold months.
ND have you looked into a wood boiler to supply heat?