The place I take the wife to is $40 for the day. They give you everything you need, a map and even a bottle of water. Although on a hot day you should still bring your own. There are cheaper places, and more expensive ones. But I like the people there, always friendly and helpful.
Now once we get the wife her own kayak, we will be set. No more rentals! Although some of the more popular places that you launch from have a dock fee. Some will even bring you back, for a charge of course.