My experience: we installed a 14K Generac automatic start generator when we moved to the country. It has served us well! It runs on a 500 gal propane tank, starts automatically every week for a test run and goes on automatically when with a power failure.
We just connected it to the house not the barn. It maintains the furnace or air conditioner (we've had to use it for both), well pump, the TV, computer, frig. I do not run the tankless hot water unit when it's on however. But we have run the dryer! You just can't have everything on at once or you have to go outside and reset it for a restart.
Essentially "life support". At max capacity on 500 gallons of propane it would run for 7 days. The longest we ever had to have it run has been about 7 hours. There was minimal gas use.
We've had to replace the battery about every 4-5 years, change the oil and filter about every other year. Replaced the 15 amp fuse a couple of times The entire set up only cost us $4500 that included installation. I saw a new Generac unit 14K at Loews the other day. It's a lot smaller now than the unit we installed 10 years ago.
The price you quoted was outrageous! Have you tried Loews or Home Depot?
