First of all, thanks to the good advice here! I learned so much by reading posts and probably would not have had the nerve to travel around the way we did without the forum guidance.
We had 4 in our group: my husband & I (3rd Riviera Maya trip), our 2nd with our 2 young adult daughters.
USA transfers for roundtrip airport to Playa del Carmen transport $120 usd. Easy to find the company when walking out of the airport through all the offers. On the way to our condo the driver stopped at a 7-11 so we could buy beer & snacks. On our return, we had an early flight & scheduled for 3:30am, the driver was there at 3:10. We were pleased with the service. Also pleased that the security guard at our Xaman Ha condo, took down our room # & last name as we were leaving.
We traveled by collectivo a few times. The first time was actually mentioned as an option by the desk clerk at the condo. I had at that point nearly decided we would use taxis. But it was easy to go to the street in Playa del Carmen where they line up, state our destination, and hop in.
A full collectivo travels fast, one with empty seats stops frequently until it is full. We found that the cost varied.
Playa del Carmen to Akumal 20 pesos/p
Akumal to Playa del Carmen 30 pesos/p. A collectivo was waiting at the highway.
Tulum to Playa del Carmen 35 pesos/p. We were downtown and waved down a nearly empty collectivo.
Playa del Carmen to Tulum ruins & return trip each 30 pesos/p. 2 collectivos were waiting on the street by the ruins.
The only hard part about traveling by collectivo for us was refusing all the taxi drivers.
We took the 9 am ADO bus from the Playa del Carmen 5th ave station to Coba for 84 pesos/p. We had considered using the collectivo, then the bus from Tulum, but getting on the bus in Playa seemed easier. We found that the bus stopped at Xcaret, Xplor & Xel-ha, plus 2 stops in Tulum--one at the ruins & one at the bus station. The trip took well over 2 hours, but it was comfortable and the stop was right by the Coba ruins parking lot.
We had bought one way bus tickets, so when we were done at the Coba ruins, the bus was not due for an hour. We hired a taxi to Tulum for $20 usd, then hopped on a collectivo. That collectivo broke down somewhere north of Akumal and it took about 15 minutes & 3 full collectivos that passed by to find room for 4 going to Playa del Carmen, however, we were in a shaded stop. As were discussing splitting into 2 groups, a van stopped with room for the 4 of us.
We felt like we had some added adventure on our great vacation.