Speaking as a native.......
If you park outside, and you have a good battery with a high cca (cold cranking amp) rating, you should not need to plug in a ranger until the overnight lows reach minus 10 degrees or so. At negative 20 degrees overnight, you will be calling AAA to get them to start you in the morning. If you can get your car into a garage overnight, even an unheated one, I would be surprised if with a new battery, you would need to have a block heater plugged in. I would also recommend that you change your oil to a synthetic type, with a 5W-30, or a 0W-30 for January and February. After March arrives, you'd never need to plug it in. Most of the really severe cold in Minnesota is way up north by Duluth, Hibbing, International falls, etc. There, it is quite common to have negative 30 degrees or more in January and February. All the motels up in those parts have plug in outlets for their guests. You will not see that in the metro area of St.Paul or Minneapolis. We are supposed to get down to -4 to -7 at night for most of next week. Mid January is the toughest month on cars historically, but for several years, it's been a little wimpy. I cant recall how many years it's been since St. Paul has been -20 or colder. If you are only going to be here six months, I'd save the cost of a block heater, and if you know it is going to be -15 some night, set your alarm, get up and start your Ranger and run it for ten minutes and go back to bed. With a good battery and good oil, you will not need a block heater. Besides, It will only cost you about 30 bucks to have a service station come out with a genterator and start you up if it is ever needed.