1 therm = 100,000 BTUs.
1 KW-H = 3412 BTUs.

So 65,000 BTUs output with a 65% AFUE) gas heater costs $1.30, while
65,000 BTUs of electric resistance heat costs $1.14. If you live in a
mild climate, where the low temperature is rarely below 25-30F, an
electric heatpump can cut the cost by 2-3. Remember that heaters are
actually rated in BTUs/hour, not BTUs.

65% AFUE is unusually low by today's standards, and 90% AFUE gas
heaters are very common and not particularly more expensive.