To get to Tulum, you will be landing at Cancun International Airport. The ride from there is about 1 hr 30 minutes to 2 hours, depending on the chosen transportation method, weather and traffic.
From the Cancun International Airport you can take the ADO bus to Playa del Carmen with departures every :30min to 1 hour for around $156 MXN (about $12 USD). Once in Playa del Carmen you transfer to a second bus (ADO, AU or Mayab) to Tulum for an additional $74 MXN (about $5 USD).
Buses from Chetumal run every hour. You can take the ADO bus departing from the ADO bus station. Buses depart from 1am to 6pm costing anywhere from 290 peso to 424 peso. Check the latest prices from the ADO website. There is also a cheaper bus, called Mayab, departing fairly regularly from Chetumal for about 220 peso. You can catch the bus on the main road (Av Insurgentes) at the Liverpool bus stop; just flag down the bus when you see it coming otherwise it won't stop. Duration is about 3 hour 45 minutes.
Buses from Cancun run quite regularly. There is also an ADO bus direct from Cancun Airport to Playa del Carmen.
Buses from Playa del Carmen run hourly or so. Bus station is at southern end of Fifth Avenue near Playacar. ADO Bus $74 MXN stops at Xcaret and Xel-ha enroute to Tulum. Mayab bus $42 MXN stops more frequently enroute to Tulum from Playa del Carmen. Both have a/c.
To visit the ruins, get off the bus at the first Tulum stop at the intersection with the access road to the ruins. It's an easy one mile or so flat walk to the ruins from the intersection.
An alternative to the buses is to catch a "collectivo" van. In Playa del Carmen you can find these on Calle 2 towards Avenida 20. A one-way trip costs $45 MXN p.p. (December 2020). Buses leave when full (a matter of minutes). Make sure to ask specifically for the ruins, as the town of Tulum is another stop. You will be dropped off and picked up at the side of the Federal Highway 307 (the same intersection where the buses stop), from where you can walk the last 850 meters to the ruins.
Rental cars are priced reasonably and are the easiest way to get around the Tulum area. Shop around rates upon arrival, and feel free to haggle. Check with your credit card company to see if they automatically insure you, most do so you don't have to pay the additional insurance that the rental agency often tries to insist you purchase. If you check prices on internet, make sure to confirm that the price you are seeing if the final, as some companies apply surcharges at the very last minute when you are already signing the contract.
It is a very easy drive to Tulum. To get there you take the only highway south from Cancun Airport straight down past Playa del Carmen, Akumal, etc. About 90 minutes from the airport you will arrive in Tulum. If staying on the Hotel Zone, you will see a sign that says "Boca Paila" and you need to follow it and turn left. From there, you just need to look for your hotel.
Watch out for police speed traps, especially as you are heading out of town, on the 40km/h section just before the highway. It is a point were most cars are accelerating and 40km/h seems innappropriate. The police are looking for money: "this infraction will need a ticket... your license will be detained to guarantee payment and you have to come to the station to collect it... it will cost 1600pesos... or you can pay now and there is no ticket...". Local advice is to not see the police when they try to flag you down. Other strategies: if you have to stop, do so gradually so there is a long unattractive distance to walk, and keep your license somewhere not handy so you can stall giving it to them; or insist on paying the fine in full at the police station which might not an attractive option due to the hassle paperwork and actual work. Carefully watching the speed limit signs helps too.
If you don't want to drive or suffer the hassle of going up and down the buses with your luggage, you can pre-book a transfer from the airport to your hotel or destination. There are many companies offering this service that are reliable, safe and professional as:
Many of the Hotels in Tulum offer a pick-up service from the Cancun International Airport for an additional price depending on the hotel. Check with your hotel and compare rates.