I use a electric oil filled heater in my RV. I leave the thermostat on low and it works fine. We don't have many real cold spells but it hasn't been a problem keeping it above freezing.
Try to find a ranch type fence builder. Ask them to do it in between jobs or on a Saturday. If you were 20 miles east of San Antonio I would do it for half that. You might also look into renting a skid steer with an auger.
I like 1/4 drive. I use it a lot on motorcycles. I'm much more likely to over tighten than under tighten. I like to use the smallest drive size that will work.