If you have a small group that can fit into a car or a van, renting a car is a great way to go. Not only can it be very inexpensive, but affords you some wonderful options.
We like to rent a car at the airport, then I'll drop Nancy and the luggage at the pier, go to the car rental counter, which is less than 3 miles away for most of the major companies, check in the car, and then take their free shuttle to the pier. When we get back from the cruise, I repeat the process in reverse.
We've rented cars for as cheap as $25 each way, but no more than $45 - depends on the time of year and any specials they may be offering, especially for AAA or AARP members. But it pays to join their frequent renter programs.
By doing this, we can go where we want when we want. We have a couple of places where we love to shop that we don't have available to us - especially Sheplers!! It's an awesome western store. But we've also gone to the beach and to Kennedy Space Center.
For groups larger than 5 or 6 people than you can fit into a van, there are some really good and fairly inexpensive shuttle services available.
But this is one airport-to-pier combination where taking a taxi is not a good option - way too expensive. There are just better & cheaper options available.