Getting Around 

Air Travel

ADO Bus

Colectivos

Car Rental

Air Travel

Best if you're going longer distances. The roads are mostly fine, great even. But the trade off of driving 25+ hours or a one hour flight are well worth it. 
I almost always use SkyScanner for my international and domestic travels, domestic flights while abroad. There are plenty of great online resources, and don't be scared to fly with the local airlines!

Here are some airlines that operate Domestically: 
Aero Mexico Volaris  Avianca 
These buses are clean, air conditioned, and play movies. 
Bring cash for the people who walk on with snacks/drinks. Not a great place to haggle, they're very cheap already and very convenient. Take your trash with you! 
Bring: Hygiene Kit  Including enough toilet paper or wipes, a doggy bag, rag or washcloth for drying your hands and a small vial of soap or a hotel soap. They fit well into a small pouch or ziplock. I always carry this kit out, never know what kind of bathrooms or facilities you might encounter. 
Tulum Ruins Stop  

Private Taxi / Car Services

Taxis

They should have their rates listed and are set prices for mileage or between zones. They're easy to read, and if you don't see one, ask. Most of these drivers are very kind and friendly. 
The taxis are color coded by town, which is fun to see!
They're very affordable, and easy to hail. Some areas cost more at highly trafficked areas like Wal Mart, but if you walk a block away you will get the regular rates. These are generally set fares and for 'prime' locations, they're not trying to get one over on you! 
Easy place to practice Spanish, as well. PLEASE Do not ask these people about drugs, cartels, etc. It's pretty rude and gives the wrong impression about us as a whole! 
I found just being relatively friendly gave me a lot of wiggle room with times, requesting longer distances and getting fare rates, like getting cabs from Tulum to Cancun for cheap! Be decent out there! 

Private Cars 

Will cost more than a taxi, but that's what you're paying for. Generally, if you want the privacy or to feel more relaxed, you'll take this. I've never used one but fares can be negotiated somewhat. Some of the people at the airport are hustlers, others have legitimately great deals. Do what you're comfortable with! 

Uber/Lift

Pros

  • Familiarity
  • Ease of use
  • Feel Safer 

Cons

  • Not in every township/city
  • Costs the same or cheaper to grab a taxi (easier/quicker at times) 

Colectivos

What are they? 

Micro buses, shuttle buses and vans that operate both in town and between towns. 

WHERE & HOW 

To Tulum / Cancun 
Here is where you go, get in line, have cash ready for snacks and paying for your ride.
This is the cheapest way to get from town to town, is safe, and can be an adventure! 
Plan ahead and don't expect immediate rides! Charge your phone or bring a battery bank, or solar battery bank.


Bring cash for this, and don't expect to have large bills broken. 
The ones in towns are marked with destinations. They collect in different areas. Keep an eye out, ask people!


Note

I was charged double and triple a couple times as a tourist (ending with $40MXN/$2USD for one trip that would've easily been $300/15USD in a taxi!-- not a big deal to me). Alternatively, you are taking up space that a local would other want to use to get back and forth to work.

Another time the driver was excited to have us, had an empty van, and basically turned into a private coach for the afternoon. I recommend just going with the flow, not making a scene and being respectful, as indignant as you might be! If you don't want to deal with it, get a car or private driver.  

Car Rental

costs

Varies; I saw between $30-75/day for a regular or economy. This is from the venders walking around to the big companies, Hertz, Avis, etc. 

issues

I booked one via Hertz. Showed up, waited two hours and they said they didn't have anything. Each agency said "I only have one left," and all had the same inflated rates. You can do what you want, some people have no problems. 
Some airports have shuttles, and if you're flying into Cancun at least, just take the ADO into town. It's cheap, easy, and will get you away from the chaos at the airport.

insurance

So, there are many resources saying a lot of things. I opted to get insurance for my first rental (which came out to $60/day in Tulum), and not for later ones. I booked with my Chase travel rewards card, which I believed to cover the rental. 
From Progressive Mexico and Canada Coverage: (1)  Be legal to drive in the country you're heading to. Some places require international driver's licenses. Mexico accepts US licenses, check your country. (2) Check your insurance coverage! (3) Make sure you're comfortable driving in a foreign country. (4) Know the rules. Ignorance is not permissible for bad or illegal acts, anywhere. 

Also: You can sometimes get coverage abroad temporarily through your regular car insurance. I have Geico, Tourist Insurance in Mexico and this is what they offer. 
There are also local and Mexican companies you could get, or just get the Point of Sale insurance. You might feel 'scammed' but insurance is required, and like all US states, varies greatly.
Anecdotally, even if you have coverage, if you can't prove it via a phone call you *could* end up in jail for the night. Not arrested, but held until all parties have been cleared. Why risk it?