General,
You also have to factor in the cost of maintaining an additional engine on the chance you might need it. You would be amazed at the number of people who buy a standalone generator and stick it in the storage shed, then drag it out when a hurricane leaves them without power. Guess what, it don't run.... and they want to take it back to the box store they bought it from, expecting a new one, or a complete refund. Bottom line, when you need one, it needs to run, and pto generators don't require an engine to be maintained as long as you use your tractor regularly. Running any generator constantly is kind of a waste of fuel, in my opinion, as the necessities don't require constant running, and if your running it for the central a/c unit, then shut it off, and open the windows.
There are ways to conserve the fuel (and tractor hours) if you want lights on all the time. A simple battery bank (take them out of your vehicles) and use an invertor to run a couple of lights. You can charge the batteries while your running the pto generator in intervals of a couple of hours to keep freezers going, or while cooking, if you don't have an outdoor grill.
David from jax