Answer to my own question:
The easiest, and probably cheapest, thing to do would be fly to Chicago (O'Hare or whatever), rent a car, and drive to Oshkosh (176 miles). Then, drive from Oshkosh to Clinton (241 miles), then drive from Clinton back to Chicago (145 miles) and drop the car off and fly home from Chicago. Messing around with regional airlines is too much of a hassle, and too expensive.
