I am trying to book the Atlantis Submarine in Grand Cayman as I've heard nothing but amazing things about it, we aren't divers but I love the ocean and my kids are really excited about being on a submarine. My question is how come its so expensive to book the excursion through the cruise ship, Royal Caribbean charges $86 per adult and $44 for our kids each. I found the exact same Atlantis Submarine trip on Atlantis Submarines in Grand Cayman and they only charge $69 for adults and $34 for kids!!! So why is it so much more to book with the ship? We'd save $54 is we book on our own, is there a catch???