A local bus (there's just one) departs from behind the market or from the ferry dock and heads along Avenida Rueda Medina, stopping along the way. You can get to the entrance of Hacienda Mundaca, within 300m of the Turtle Farm (Tortugranja), and as far south as Playa Lancheros (1.5km north of Playa Garrafón). It's a cheap ride at M$5, but expect long waits.
Inspect all scooters carefully before renting. Costs vary, and are sometimes jacked up in high season, but generally start at about M$250 per day (9am to 5pm).
Many people find golf carts a good way to get around the island, and caravans of them can be seen tooling down the roads. The average cost is M$550 per day (9am to 5pm).
Mega Ciro's Scooters and golf carts get good maintenance here.