Cruise Ship Companies mark up the shore excursions by an insane amount. Its always cheaper to arrange things yourself. I agree with the comment about security concerns is some places in the world but definitely not in the BVI. The only time I would recommend paying the vig to the cruise ship is when you may be pressed for time returning to the ship. When the cruise company arranges the activity, it is their responsibility to return you to the ship. If you are delayed, they will either hold the ship's departure or arrange a rendezvous underway. If you do it yourself and something goes wrong you will have a big problem!