[0] https://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=W...
In the SF Bay Area, our last PG&E bill split across Jan/Feb was effectively $3.05/therm. The actual pricing in our bill reflects tiered pricing, with different tier thresholds in each month. The first tier covers up to 2 therms/day in Jan and 1.48 therms/day in Feb. The price tiers were $2.68..$3.06/therm in Jan and $2.75..$3.14/therm in Feb.
The bill also described $1.37/therm and $1.44/therm procurement prices for Jan and Feb, respectively.
It used to be much cheaper so a lot of old houses that aren't near a natural gas line were built with propane heat. You might save $200-1000 a year by switching to a heatpump but that means 10+ years to offset a ~$10000 install cost for a large unit professionally installed with a new 220 circuit run for it etc so most people just keep paying for propane or maybe use small electric space heaters.
And if you are somewhere you need to worry about pipes freezing in power outage a while you are away or temps bellow the heatpumps minimum -15f range a propane stove is a nice option. Relatively cheap to install and they can be setup to run on a thermostat with no grid power.
If i was building a new house i'd go heatpump + a propane stove for back up heat and a dual fuel induction/propane range.