Three years ago we rented our own jeep in Aruba and didn't pre-book. We heard that they might sell out so we were sure we were about the first people off the ship and walked quickly along the dock and saw the rental office. Sorry that I can't remember the details, except that it was $60 for the whole day - a car would have probably been cheaper but the jeep was more fun. We used a credit card and had to gas up. It was the first time we had encountered having to pay for gas in advance before the pump would work.
We got a map, drove along the hotel zone, and then the opposite coast line, where we were surprised to see that the road was dirt and bumpy. Don't wear a clean white shirt! The wind blew the dust into our clothes and my shirt was never the same again. . The water on that side was rough and rocky, but neat to see as you drive in desert-like surroundings. The jeep caravan from the ship caught up to us and we followed it for awhile. We stopped to see some sights along the way, lost the caravan and followed a tour bus for a bit. Got back on track with the map and drove to the southern tip and back to town. Parked, had lunch. Drove back up to the hotel zone and swam at a great beach (Palm). We returned the jeep late afternoon. Walked downtown, poked around and visited a casino (hey, they had a bathroom) and walked back to the ship. No problems. The jeep wasn't in great shape - old and bit dirty, no radio, no top, but we had alot of fun. The island is only 19 x 6 miles wide and the roads were fairly good - not too fast or intimidating. Plan to get lost. We laughed and smiled alot and would do it again.