OK so not a bus tour but the closest thing, and even better in some ways. The tour is not very expensive as far as I can remember (don't know exact price). It was probably around $50, don't quote me. The tour takes a few hours making a one stop at the top of the hill (after which you can continue the tour on the next carriage available or wait around for a bit (you can go to the butterfly conservatory).
by Chengbuck on August 18, 2006
Carriage Tour
Mackinac Island Mackinac Island, Michigan 49757
(906) 847-3307