I live in Harford County in an all-electric home.

The cost of running a heat pump in the winter varies with the outside temperature. As outdoor temps drop, the btu's produced from the heat pump drops, and the C.O.P. (coefficient of performance) also drops. COP is the efficiency of the heat pump.

At 32F outside, a typical heat pump has a COP of 3.

Cost of 1 million btus at 13.5 cents per kw-hr, COP = 3:

(1,000,000 btu / 3413 btu per kw-hr) x $.135 / 3 = $13.18.

So the cost of 111 million btu = $13.18 x 111 = $1464.

Don't be fooled by SEER. 44% of the value of the SEER calc is at 67 and 72F outdoor temps. I don't run my a/c at these outdoor temps. EER determines your true cooling costs. Whichever SEER system you get, you want 12 EER and 9 HSPF minimum.

Also, because you are looking at a heat pump, you want full btus at the 47F rating temperature. Anotherwords, a 3-ton system should be 36,000 btu, not 33,000. Some condenser/coil combos are weak on heating btu's. The Trane XL16i is notorious for weak heating btu's.

Good luck.

there is no question that you should get a heat pump. The costs difference to go from an AC unit to a heat pump is minimal (maybe $500 depending on...). You can set up your system to use the heat pump down to a certain outside temp (maybe 35°) and then use oil below that. The heat pump will be used in the mild weather when it is most efficient. The only catch is the air diffusers and grilles might not be installed for a heating system so some adjustment may be needed.
The cost for a million btu at 82% efficiency and $3.60 gal for oil is $31.81.