Ck the prices.they will not be double maybe 10 or 20 dollars more but that includes transportation.Just remember if you dont make it back in time the cruise ship will not wait 1 second for you unless you booked it through them.All the dive shops I talked to would not pick you up.You had get your own ride to their shop.Also most dive shops will not work around the cruise schedule.But call the dive shops and ask what they can do for you.Good luck