I noticed the spike at MSP too. I am trying to take advantage of the NW miles to go promotion and found that I can't get a car for any day in July for less than $50-60/day on airport. My last rental was from National less than a month ago ($26 all in) and I got lectured for bringing the car back early because they were paying to park several hundred cars that weekend. I found similar prices at neighborhood Enterprise locations but my primary goal is not transportation I am passing.