I FLOVE Mackinaw, my dd calls it "her" island, so I think you'll have a great time.
Bring your own bikes if you can, its cheaper than renting. Renting bikes by the hour = $$. You can see how much the ferry lines charge to bring your bike over online. Star Line, Arnold and ... I can't remember the third one... are the ferry companies.
You can stay at Mission Point reort, the very expesive Grand Hotel, the Perry Hotel or a slew of b&bs on island, or any chain hotel in Mackinaw City. Staying on island is pretty pricey, so we usually stay in Mackinaw City.
How long are you planning to be in the area? Here's what we usually do:
1. One day totally on island. We shop, go for a carriage tour, see the butteryfly house, bike the perimiter of the island (8 mi of flat roadway, very nice), maybe visit the fort, browse the gift shops.
2. Visit Tahquamenon Falls and Whitefish point in the UP. Its about an hour or so from the bridge and the falls are quite beautiful.
3. Visit the big outdoor mall and downtown area in Mackinaw City and hang out there awhile before heading home.
Have a great time, I can't wait to head up there again in July.
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