How long does the person intend living in the house? If any way medium to long-term, i think any form of heating by electricity is going to costs much more than heating by natural gas. The house sounds ideal for a combi gas boiler.
The first priority should be insulating the house to a high standard so that you need less heat in the first place.
NG, if available would be say 5 cents /kWh, and say oil is 8
Night rate elec might be 10, COP for the HP of say 3, so 3.33 vs 5 or 8