Whether you book your P&O excursions now or on the ship, the cost will be the same. However in most Caribbean ports, there are always lots of local taxis who will do you a tour or whatever you want cheaper than the ships tours. They all deal in US dollars so there is no need to change into local currency but make sure the quote is USD and not local dollars. The French islands have the Euro.
Doing it yourself will be much cheaper and you will get much more choice. You also don't have to wait until you get there, as you can pre-book tours directly with legitimate operators on the Islands (we have been on several excellent ones). I suggest you do your research online and to start you off, if you put "cruising Spencer-Brown" in a search engine and explore the results for ports of call you will get many recommendations. Have a great trip.
Try looking at the P & O community site for shore excursion details, both theirs and independent.
Hi, we did a Caribbean cruie a couple of years ago with princess and are going again on the 13th march. We did all our own excursions exceptone. There are always taxis and mini buses at the ports and u can haggle with some over prices. There are usually a few who want to do the same tours so u find that it works out cheaper than the ship excursions. The guy we had in Barbados was brilliant. He took us in he morning up to where all the celebs have their homes and the famous Sandy Lane then he took us back to the ship for lunch arranged to pick us up in an hour then took u to the beach where he introduced us to the guy who made sure we had sunbeds, cocktail etc, picking us back up around 4.30 to take us back to the ship. I cannot remember what he charged but it was not expensive and far far cheaper than the tours with the ship. have a great cruise, I cannot wait to go back.