There are car rentals near the cruise port in Curacao Port. In fact, at this port, some of the car rental companies actually directly meet the departing cruise passengers as they come off the ship. In Curacao Port, there are 2 major docking ports. These are known as the Mega Port and the Mathey Wharf. The Mega Port is generally reserved for bigger cruise ships, while the Mathey Wharf is designated for smaller ships.
For more info, see Curacao Port Guide