Most of the airboat tours, by nature, are away from the general tourist area as they need a large, swampy area to tour.
If you can rent a car for the day, I highly recommend Wild Willy's. We did their tour on our Christmas trip and it was one of the highlights of our vacation. You can see my full write up and tons of photos by clicking on the trip report link in my signature. The airboat portion of my report is on page five and begins at post #73.
Wild Willy's is located in St. Cloud, though, so it was about 30-45 minutes out of town.