Hi Jim
Our group of 3 older adults just returned from Riviera Maya. Our primary reason to visit the area was to visit the Mayan ruins. We took the simple method, having done absolutely no research ahead of time, and booked a bus tour at the resort when we got there. The company we booked through was Mexican Travel; cost is $87 each discounted to $60 if you endure a timeshare sales tour which we didn't do. This includes coffee, juice, pastries & fruit served during the morning ride, a guide the entire time including at the ruins; a stop on the way for potty & shopping; several hours with guided tour at the ruins; buffett lunch in Vallidolid, a visit to Ik Kil Cenote, beer & sodas during the bus ride; & all admissions & road tolls. We were picked up at our resort at about 7:40am & got back about 8:15pm. The large bus was full but comfortable & we enjoyed meeting some of the others on the tour. Our bus picked up folks from 4 different resorts.
A private van would definitely cut time off the long day but the ride was interesting & the route in was different that the route to return. Having a guide at the ruins was a big plus. Ours was a wonderful older man named Miquel who is Mayan & spoke 6 languages & has studied this fascinating culture all his life. Chichen Itza is huge & it's like trying to see Yosemite or Washington D.C. in only a few hours. No matter how you get there, it is a long drive. If you do book a tour, I would make sure you have a guide in the park. Wandering around on your own will not be as good an experience as having someone to tell you what all the buildings were & interpreting the symbols. It was a very good tour & we think worth the price. I wish I had read up on the Mayans a bit more before our visit.
Any questions, feel free to ask. Have fun.