From Traverse City to Mackinac City is about a 1 1/2 hour drive on two lane roads, but very scenic. Once you get to Mackinac City the ferry ride is fast to the island, about 20 minutes, or 12 minutes on the hydrofoil on a smooth day. The Grand frequently has specials for the spring and fall, outside of their normal tourist high time, which is in the summer. Spring and fall nights can be found for $400 per night, check
AAA rates, and yes, it includes breakfast and dinner. You also get the carriage ride from the dock, as there are no motorized vehicles on the Island. Everyone walks or rides bikes. You can take your bike on the ferry, or rent them on the island. The rooms are smaller than what most of us are used to in a hotel, and there are no TV's in the rooms. Going to Mackinac Island is like stepping back a century, and the nights there are SO-O-O quiet. Days are noisy, though, since most people go over to the Island for the day. The ferry is around $25 per person, and downtown is a short walk away, where you can buy your fudge. Tourists in Michigan are called "fudgies" because tourists buy so much of it, and it is good. Mackinac Island is known for their homemade fudge.
By the way, there are other hotels on the Island but they are all expensive. Many Michiganians go the cheaper way, staying at a hotel in Mackinac City, and taking a day trip to the Island. Hotels in Mackinac City can be found in the summer for $100 per night. If you are "into" historical things, the City and the Island both have forts and reinactments. The fort on the Island played a pivotal role in the War of 1812, where Britain took over Michigan without firing a shot. They dragged a cannon up the hill to the fort, and threatened to fire it, so the Americans surrendered. The problem was that Britain had no cannonballs for the cannon!