Only a few? I just searched Google Maps for "camgrounds near Champlin, MN." Looks like plenty of places near by and more the futher you zoom out. While riding ACA's Northern Tier route we didn't have any problem fiding places to camp during our 14 days in MN except for the two days in Minneapolis, which was off route, and the two days we spent at the HI hostel at Lake Itasca. We even camped for free at the city park in Grand Rapids.

Also...Does your $40/day take into account the money you will not be spending because you are touring? For example, I usually buy my lunches out during the work week. I also tend to buy fresh, more expensive dinner ingredients when I am home compared to when I am touring, and I usually eat out at least once a week when home. If you drive to work every day (I walk) you won't have gas costs if your tour starts and ends at home.