Lots of people just rent scooters to get around the island. I must say that I was tempted, and might be tempted again.... However, lots of people, both locals and visitors, die in moped accidents on Coz. It looks like fun, but in fact you will probably get the crap scared out of you, even if you are an experienced biker.
If you want the independence of self-drive rather than using taxis, consider renting a car. Make sure you book ahead as demand often outpaces supply. Don't think you can rent a car in Cancun and take it over on the ferry--by all reports, it's fraught with frustration and difficulties.
Taxis are the easiest way to get wherever you can't walk in Coz. When you arrive at the airport, you will need to go to the little booth in the arrivals hall to pre-pay your fare to your hotel. It won't cost much since the airport is just a ten-minute drive from San Miguel.
For every other trip you make in a taxi, just flag a cab down in the street (it costs less than if you pick one up in front of a hotel), tell the driver where you are going, and he'll set the price, which works on a zone system.
One-way airfare from Cancun costs about $70 US. If you aren't worried about schlepping a heavy bag of dive gear from the airport to the bus then the ferry and finally to your lodgings once you arrive in Coz, you might consider saving that money (for two more dive boat outings with four more tanks of compressed air) by taking the ferry (there's a separate tip about that).
Taking the ferry straight from the airport requires a fair bit of patience, though, if you opt for the economical path, so you should consider your options and weigh the cost/benefit balance carefully.
If you stay near the downtown area, as I did, you only need your feet to get to most places. To go further afield, like going to the Mayan ruins or the east coast beaches, you will need wheels, though.
FYI so you get an idea of the walkable domain of San Miguel, enlarge the map in the photo. The place I stayed--Vila las Anclas--is shown with a blue checkmark.
One way of getting to Cozumel is by cruise ship--up to 5 or 6 a day dock there sometimes. You might be lucky if you dock right in the town of San Miguel as there is space for about 2 large ships there. Otherwise you'll end up a bit south of town and will have a considerable walk to town or have to take a taxi.
A fun way to get around the island is by scooter. There are many places in San Miguel where you can rent them, and it should run about $35 per day. The traffic is a bit heavy in San Miguel but once out of town, it is a pleasure. Just be sure to watch out for the many speedbumps which are sometimes not so clearly marked....
There are two different hydrofoils running regualrly between Cozumel and Playa del Carmen on the mainland. It's quite easy to do a day trip from Cozumel to playa del carmen or vice versa. Tickets are sold right at the pier in San Migeul, Cozumel.
Definitely take a taxi to and from the Tampa airport -- it is cheaper and much faster than the cruise line's transport. It will cost approximately $20 for a cab or $25 if you take a taxi minivan. Carnival's transport charges $28 round trip per passenger. It took us 20 minutes to get through the lines at embarkation (we arrived at 11:30AM).
It seemed Carnival did everything in their power to get you through and onto the ship (be sure to complete all the paperwork Carnival sends you before arriving at the port to save time). Then we spent in the holding area about 1/2 hour.
If you intend to travel around the island of Cozumel from the tourist center, renting a car is priceless! If you walk in to any budget rental care store front you can rent a jeep, suzuki, or VW safari (which was a blast) for the equivalent of 40 dollars a day. All of the sand beaches, Mayan ruins and the most beautiful remote parts of the island are pricey to get to by taxi so you end up saving money in the end. Also, it is impossible to get lost because there is only one road that goes around the driveable part of the island.
There are several ways of visiting Cozumel. I flew from Toronto twice, once direct and once changing planes in Cancun. The first flight we still touched down in Cancun, went through customs and got back on the plane. We were dropping Cancun passengers off that's why we had to stop there.
Another way is by ferry from Playa Del Carmen. It's a fairly cheap trip and many do day trips to and from the mainland this way. The ferry terminal is right in town in San Miguel, so once you get off the ferry, walk straight and the main square is in front of you.
You might also visit Cozumel on one of the many cruise ships that visit this port. It's quite a popular stop though the ships are damaging the reef since they've had to build newer docks for the ever expanding cruise ships.
To get around the island I would suggest renting a car unless you feel like renting a moped. A car is preferable to me as I was hauling my snorkelling gear with me, plus the top on the car was very handy since I once visited during the rainy season. I will say that my little VW Bug didn't have side windows so I still got wet. It was a convertible so I could take the top down if I wished.
It doesn't take long to circle the island so unless you plan on driving to and from your resort I wouldn't suggest getting a rental for more than a day or two because parking in town is a pain in the butt.
There's only one or two gas stations on the island, so watch the level in the tank.
You could do what I did to get a free car rental and that was to sit through a time share seminar. I was by myself and bored anyway, I knew I wasn't going to buy into it. But I did get a free lunch, a free blanket, free bottle of tequila and a day's car rental out of my time, so it was well worth it for me.
Pictured is my rental, very cheap car, the truck locked with a padlock, lol! But hey, it got me from point A to point B and that's all that mattered ;-)
Taxis are plentiful on the island and not expensive. However, the drivers will cram people into the cabs or limo (not, repeat not a limousine) and drive 100mph to get as many fares in a day as is possible. A real roller coaster ride. But, I never saw an accident, just a lot of one finger salutes.
If your going to take a tour rent a Jeep. It's not as exciting, but it's cheap.
Since its an island, you'll have to fly in or sail in. It is a cruise port. I flew in on AeroMexico.
Taxis are very easy to find or rent a car. and if you're REALLY lucky, you can rent a VW Thing with flames, one headlight and no windshield wipers. Vroom! Vroom!
When going to the Far Ceralain, make sure to park on designated areas and follow directions. There are park enforcement people there but not sure if they give tickets for illegal parking.
Cozumel is a popular stop on cruises in the carribean, but we flew there direct from Newark, NJ.
Rent a jeep or a vw bug, they are a must have!