I used the U Rent Em Canoe Livery in Hastings, Michigan for my excursion. They claim to be the oldest and largest livery in Barry County. They have some of the best pricing of any livery and the distance from Grand Rapids is reasonable. Their prices were $30 for a canoe and $20 for a kayak. The best part of the rental is that the cost is by the day. They drop you off near Hastings Lake and let you float back to their trailer on the river. If you wish to continue to the airport, let them know and they will pick you up there at no cost. Get there early and prepare for a day of boating. The first leg is about 3+ miles and the complete journey is about 7 miles.
As for the river itself, the river starts out wide, stagnant, and slow. There is tons of algae floating like speedbumps in the river. Don't be deceived. Once you get into shallower water with stonier bottoms, the river becomes reminiscent of the Pere Marquette River with hairpin curves and treed overhangs. The water clears up and is nothing like it's downriver persona. Be sure to pack a cooler on hot days. The trip is long and you need to keep well hydrated. I learned this the hard way. The fishing is good and you will see a lot of fish in the water.
For a day of canoeing, fishing, and floating, the Thornapple is a well-kept secret. Combined with U Rent Em's prices, this is a great one-day vacation within distance of Grand Rapids. Be sure to try out the river and check out U Rent Em's website here.