I have both rented a car and used an Uber. If you plan on staying on the island, I would recommend an Uber. It was 50ish bucks and had the medallion to cross the bridge. The resort has bikes if you want to explore the island. If you are going to want to go back to Fort Myers, I would probably rent a car.
When you leave the airport, turn right. Turn left on Daniels and go West. Put the address into your gps and it'll take you directly to the resort.
We rented a car for the weekend. If you're flying into Fort Myers, Sanibel Island is about a 30 minute drive with a paid toll bridge on entry. If we didn't have a car rented, I suspect an uuber or cab could get you there at a cost, but it'd add up quickly if you're planning on needing it often to get off the island. The island itself is very bike and walk friendly.
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