The issue you really run into is that, even at idle, the generator burns a fixed amount of propane. The minimum is about 2 gallons per hour. Which is roughly $6
So you can imagine that, for 3 days of usage, $500 provides a strong incentive to seek out alternative sources of power.
We run about $1200 a year in propane costs for the generator, estimated.
All the loads that I might consider a generator for are intermittent (well pump, fridge, microwave, space heater).
I've wondered if it would make sense to get inverters for the fridge, microwave, and heater and get a pool of batteries, and just use the generator for charging batteries and powering the well pump.
With a sufficient number of batteries in the battery pool it should be possible to only need to run the generator when there are sufficient batteries to charge that the generator can run at its most efficient output.
At that point the generator will only run if the batteries dip below e.g. 20% charge, making it extremely affordable.
A gallon of gasoline produces about 36 kWh, and costs about $3.6. Assuming that the motor + generator + inverter chain has efficiency is 25%, it's 9 kWh of electricity per gallon, or about 40 ¢ per kWh. Likely twice as expensive as the grid, but fine for a few days.