It's only an 8 mile trip so the cost will be minimal. I always take a cab, too impatient to wait on a bus for all the pax and luggage to be loaded. Taking the cab will have you at the pier, in line and probably onboard before they even get that bus loaded in many cases. Good choice.
I just didn't want our cab fares to break the bank. Everyone tell's me to stay on South Beach so I really didn't want to give up the experience there, since we will have two days there.