Hey Tommy,
Happy Thanksgiving
I tent campped there for New Years week, but it was about 8 years ago, so I may not be much help. I was back once for a day trip about 2 years ago. My main memory is that is was unbearably hot! I doubt that has changed. We stayed in the water all day which was ok, but had to get up several times at night to cool off. Also there was a terrible raccoon situation in the campground. They were everywhere. Would knaw through tupperware left outside and knaw though tents if anything that smelled like food was inside.
It is a nice park; the facilities are excellent and they have developed a nice underwater playground. Butch is correct--you cannot swim to a reef, but they have a historic underwater trail accessable from the beach and of course, lots of critters come visit.
Dunno if you are familiar with FL state parks, but the usual problem is getting a site. In general it is first-some-first-serve whivh means a lengthy line at the crack of dawn and frequent dissappointment. Some will now reserve a limited number of sites.
I was diving both times and took a snorkle trip once. I don't remember exact prices, but it was not expensive--$39 sounds reasonable. They are 2 tank trips, but a very short boat ride. They did charge extra for any thing you needed from them including tanks &, weights. It is fairly shallow, but very colorful. Sadly, the reef does show evidence of heavy use. The boat captain was quite nice and accomodating. Dives are not lead--they give you a set time to be back at the boat and you are on your own. They will buddy up any single divers.
Have a great trip!