I found some suggestions further down in the section. I had this same question last year when considering the Carnival Liberty. I was going to fly in the day before and the Carnival transfers wouldn't work. I've seen some recommendations for this
service. I've never tried it though.
Since I know you have cruised on Carnival before, I'll give you their transfer prices just in case to compare. One way $30, Round trip $60, per person. I'm not big on the cruise line transfers mind you, sometimes they can be convenient though. I hope you get some more ideas.