Ok, I mentioned I would investigate this excursion. Here is the scoop so far. I'm looking at how the numbers add up compared to Disney. I contacted Fantaseas directly and they indicated they do offer a discount to Disney, which when I add the numbers, may be the case.
St. Maarten to Anguilla Fantaseas Dolphin & Stingray experience
priced separately:
taxi from dock to ferry - ?
ferry from St. Maarten to Anguilla - $20/per person, round trip
http://link.ai/
taxi on St. Maarten - ?
fantaseas experience - $125 (if booked directly, regardless of age)
http://www.dolphinfantaseas.com/
lunch on St. Maarten - $10/per person
That adds up to $155 so far, without the ? fares.
From Disney's website:
Anguilla Dolphin & Stingray Encounter (7 - 7.5 hours)
Swim, feed and play with dolphins while learning fascinating facts about them. There will be plenty of photo opportunities, so don't forget your camera (underwater cameras are not allowed in the water). For a perfect ending to a memorable morning, take time for fun and sun on the beach at beautiful Meads Bay, where you can enjoy an authentic Caribbean barbecue lunch.
Adult Price: $180 (ages 10 and above)
Child Price: $158 (ages 5-9)
Departure Time: 7:30 am
http://disneycruise.disney.go.com/disneycruiseline/funonshore/excursiongroupingindex?id=MaartenExGrping
Usually it is considerably more cost effective to do excursions on your own, however for the minimal price difference of $25 or less, I would be inclined to book through Disney on this one.
I'm curious why this excursion hasn't been mentioned as having been done on the boards - I've seen questions about it, but no one mentioning they have done it.