I settled for seat warmers.
My wife has heated seats in her car and wishes that my truck came with them, too. Alas, at my truck's trim level, they were a very expensive dealer add-on.
A friend in college who was from Iowa had a block warmer and a electric heater inside his car. I don't know what it cost his parents in electricity, but he parked it outside and said it was the only way to actually keep the car drive-able.
The block heater was a factory installed option on my truck. There's even a small storage bracket for the power pigtail. The rule of thumb here is to plug in below 20°F (-7°C). Typical power consumption is in the neighborhood of 1000-1500 watts, so I run mine with a timer, three hours before I start my morning commute.
I've been told by slope workers that during winter months, vehicles are run continuously (even when parked for extended periods) until they are garaged. Friends in Fairbanks have told me it's not unusual for flat spots to setup on the tires of cars parked outside until they've been worked out with a bit of driving. During my first winter here, we had temps around -30°F in my neighborhood. My vehicle at the time had a manual transmission and putting it in gear that morning was like stirring lukewarm tar.
