I live in St. Simons Island, about 45 mins away from Jacksonville. There is a private island near us called Little St. Simons and it has 16 miles of beautiful beaches, isn't crowded, and they can even stay there for their honeymoon.. they have an all inclusive resort type thing where you can stay in a cabin and they make you breakfast, lunch & dinner and you can go horseback riding, fishing, etc.. it's $299 per couple per night I think, but that includes everything...all you can eat food, open bar, lodging, etc..
A family from New York owns the island but it is open to the public.. and I think it would make for a perfect wedding and it is only about 45 miles away from Jacksonville.