There is no regular bus service to María la Gorda. If you are coming, check with the Gaviota hotel chain, which runs the only hotel here -- they can arrange transportation to and from Havana, leaving daily at 8am and returning at 2pm, for CUC$60 per person one way, or CUC$100 round-trip. (It becomes cheaper the larger the group.)
To get here by car, take the Autopista Nacional (A4) west to Pinar del Río. From Pinar del Río, it's another 94km (58 miles) to María la Gorda on the old Carretera Central passing through the prime tobacco-growing towns of San Juan y Martinez and Isabel Rubio, and then continuing on to Sandino and La Fe. There are two left turns on the route without signs, so you will need to seek directions. You'll hit the water at Bahía de Corrientes at La Bajada. The road to the left leads 14km (8 3/4 miles) to María la Gorda. The road to the right heads out the peninsula another 59km (37 miles) to Cabo de San Antonio.
The Marina María la Gorda (tel. 48/75-0123) is an official entry and exit port for yachts. When arriving by sea, contact the marina before entering Cuban waters (19km/12 miles offshore) on VHF channels 16 or 19, or HF channel 2760. Theoretically, there's a Customs and Immigration officer on 24-hour duty, and water, electricity, and fuel can be had while tying up to the small pier here.
Vía Rentacar (tel./fax 48/77-8131) has a car- and scooter-rental desk here. A four-door compact car with air-conditioning will run you between CUC$55 and CUC$80 daily, including insurance and unlimited mileage, while scooters go for CUC$24 per day; hourly rates are available.