I've been to Cancun and Tulum which is further down the coast. Playa del Carmen is roughly in between the two.
You'll be able to do an excursion to Chichen Itza without any problems. There will be loads of companies in PdC running trips and I'd be surprised if your hotel doesn't offer a way of booking it through them.
If you're the type who enjoys trips out, I'd recommend Ek'Balam which is another Mayan ruin site and is a lot less busy than the CI. You can actually climb the pyramids there and from the top you overlook the jungle which is a stunning view.
When we were there it started to absolutely hammer down but we stayed at the top as everyone else headed down for cover. The rain lasted for a few minutes and after it stopped, the noise from all the various creatures in the jungle was astonishing to hear. Howler monkeys, birds, insects all crying out in chorus.
Valladolid is an old colonial Spanish town and worth a wander. My wife and I really like the old Spanish colonial towns and stopped for lunch there.
One thing I regret is not getting a chance to visit one of the cenotes. A cenote is a natural 'sink hole cave' which is full of water and acts as a natural swimming pool. Cenote Dzitnup is the most famous one and was just closing when we turned up. I'm gutted we never got to experience it.
We hired a car and it was pretty easy driving there. Getting out of Cancun was a bit frantic but then the roads were dead in between locations.
In answer to your question on prices, I reckon they'll rocket as soon as this traffic light system is introduced, that's why I was willing to take a gamble.