You really need to be calculating costs based on seasonal performance (SCOP) which is going to depend on your area. In my climate the worst case COP is around 2, but the seasonal performance of an air-to-water heat pump would be between 3.5 and 5, depending on various factors.
Granted it doesn't make a difference in your example because your gas is cheap at $0.05/kWh, but for me (EU), the price for natural gas would be around $0.11/kWh while electricity is around $0.25/kWh.
Granted it doesn't make a difference in your example because your gas is cheap at $0.05/kWh, but for me (EU), the price for natural gas would be around $0.11/kWh while electricity is around $0.25/kWh.