Please check my math...
If my home losses 80000 BTUh, and I live in a region with 3784 Heating Degree Days, then I use 7,265,280,000 BTU per year.
(BTUh x 3784 x 24)
Which is 72652.8 Therms per year.
(BTU / 100000)
If I pay 113 cents per Therm, then my base cost without factoring AFUE is: $8209.77 per year.
(Cents per Therm x Therms per year / 1000)
This figure seems pretty high to me.