Captain Heinz - Cab Ride to Dock

We are sailing on the Summitt and will be In St. Croix Sunday March 30th. Have heard mostly good things about Captain Heinz trip to Buck Island so are thinking about that. Cost analysis

Big Beards: 9:30 - 3:30 (including lunch) $99 pp + $16 pp cab ride.

Captain Heinz: 9:00 - 2:00 (no Lunch) $65 pp + $35 pp cab ride.

Net delta is $15 per person less to do Captain Heinz, little bit shorter and no lunch (or rum).

It sounds like Captain Heinz is a little more personal snorkeling trip - but why is cab so much more. and does anyone out there, who has done captain heinz before have an alternate way to get to the dock that the noted taxi? Is car rental an option? we have never been to St. Croix before.

Any info would be much appreciated.