Not meaning to be flip, but I would recommend either a rental car or checking out the Amtrak Empire Builder (trains 7 and 27) which runs through both Minneapolis and Williston ND. The train is running tonight, leaving MSP at 10:20 pm and arriving in Willston at 11:07 am. the next morning.
I happened to see this train running westbound in the vicinity of Cut Bank, Montana last week (I drove US 2 from Spokane to Fort Belknap Agency, MT; the train tracks it uses are generally right next to US 2). It conveys a sleeper car as well as a coach car.