We've always rented bikes. It's such an easy ride to the beach, it makes for a nice trip. We've rented only through Disney but I will tell you, one year, the bike I had was jinxed. Not once, but twice, I had major problems with them. There is a bike rental shop right on the way to the beach. I can't recall the name of it but when my bike broke down a couple blocks from there -- they were awesome in helping us out. Not only did the let me use one of their bikes to continue our ride to the beach, but they took care of calling Disney and arranging for a replacement bike. All we had to do was stop on our way back and switch the bikes. Lesson learned -- always carry our cell phone with just in case.
A pontoon boat would not be bad. It's much smaller than some of the larger boats that go out on tours from Shelter Cove. I know they are a lot more economical, but those big boats with probably 100 people on them, if not more, can't possibily get close to any of the dolphins or wildlife along the shore. I'll be interested in hearing how you enjoy it when you get back.