Many travelers don't realize that the closest airport to Tulum is in Cancún, which is nearly a two-hour drive from Tulum. There are countless car services, buses, and shuttles to get you to and from the airport, but they can be pricey (the service we use usually costs a little less than $200 USD for round trip).
Another option is to rent a car and either pick up in Cancún or pick up once you get down to Tulum. Because there are so many things to see and do not just in Tulum itself, but in the surrounding area, having a car makes it quick and easy to get to all the places you want to go. The price for renting a car can vary (one POPSUGAR editor rented one for around five days for about $180 USD and another rented one for just under $200 USD for seven to eight days, which isn't bad at all), but it really depends on where you go to rent and what deal you get at the time. Renting a scooter or bike for taking around Tulum beach and Tulum town is another smart option!
If you don't want to rent a car, Tulum is still totally doable by cab, bike, scooter, and even foot.