DO NOT use the cruise line unless you want to pay double. For Cozumel you can call Sand Dollar yourself if that is who you chose. I recommend calling Raul at 011-52-987-872-2786 he will arrange for a very fast boat to pick you up, take you diving, and get you back to your cruise on time. Another option is look up Dive with Martin...a great group to dive with. They will also pick you up.
From my experience the charges for a two tank dive including pick up and drop off is less than $80 per person. Just let them know what cruise ship, arrival, and departure times...they will handle the rest. Good luck.