This page has details about Jekyll Island.
A $6 entry fee to the island is mandatory and is good for 24 hours. If you enter on Friday afternoon, go on the rides Saturday morning, take the bus to the cruise on Saturday afternoon, then leave on Sunday morning, you will have only paid out $6 for the entry fee.
Jekyll Island is an animal sanctuary. There are many deer (and other animals) on the island and they are not afraid of vehicles. Please be careful when riding around the island.