I don't even want to think about taking a taxi. The cost would be likely be very high.
More reasonable would be to use a towncar service (prearranged). I'm sure someone will provide details and recommendations. The cost will be still be considerably more than $40, but it would be a nice splurge, and you wouldn't have to deal with dropping off the car and taking a shuttle back to the port (with all your luggage).
You don't say how long your cruise is. If it's a 3- or 4-day, another option may be to rent for the duration of the cruise and park it at the terminal. Depending on what rate you can get, it may still be cheaper than a taxi or towncar even including $10/day for parking. And you don't have the hassle of dropping off, shuttle, shuttle, pickup. When you get off the boat you can just hop in your car and drive away.