Welcome aboard, Janelle! My family had such fun experiencing the dolphin swim at Blue Lagoon a few months ago! I highly recommend both the swim and the encounter at this particular location, as it was simply amazing for our family!
I always recommend booking Port Adventures directly through Disney. They take care of the details and ensure that the ship always knows where you are, so there's much less worry about time management and rushing to get back to the ship in time. The
Blue Lagoon Dolphin Encounter is a great adventure! Disney offers transportation which is one reason why your three year old will pay for this adventure. Though you might be able to get transportation separately from Blue Lagoon, it won't be as easy as it is with Disney. The guides meet guests onboard Disney's ship, sign you in and your entire group walks off together to a smaller catamaran that is waiting just on the other side of the dock. It really doesn't get easier than that! Add to this the fact that after your dolphin encounter, your whole family can stay and enjoy the rest of the day on Blue Lagoon Beach. There are a few different return times from which to choose with Disney, so you can stay as long or as short as you'd like after your adventure. We loved relaxing on the beach and exploring the island after we swam with the dolphins. Also, I don't know for sure, but if you book with Disney, you're more likely to have a smaller group in your adventure than booking straight through the company. In November, my daughter and I only had two other guests on our dolphin swim at Blue Lagoon with Disney, meaning so much more interaction time for us!
I hope that gives you a bit more insight into the cost difference, Janelle. Letting Disney take care of the details will make all the difference and make your day so easy and relaxing! Happy planning!