It might seem like a lot but it's not. Look up the amps specification for the heat pump. It might pull 10-15 amps at the peak of its duty cycle. At 220V, that's 2.2 to 3.3 kWh/hour, or 36 to 59¢ per hour of heat (10 or 15 amps times 220V for one hour = 2.2 to 3.3kWh at 18 ¢/kWh = 40 to 59¢).

If it runs half the time that's $144 to $212 a month (rounded: 30 days times 12 hours/day x 40 or 59¢ per hour). If it ran all the time that would be twice that. If an 120btu/hour (roughly 1 gallon/hour) oil furnace ran 12 hours a day at the current state average of $4.50/gallon, that would be $1600.

The only thing cheaper is firewood.