Hello, I am going to be staying in Playa Del Carmen in May. I heard I could take a "collectivo: to Tulum ruins which would be cheaper than a tour. Is this accurate? Also was wondering if I should book a Carrieban Cruise now or when I am in mexico? I am looking to do as many activites without the extra cost as I am travelling with (2) college kids...any ideas ? I want to take public transportation maybe go to Island Mujeres or Cozumel by ferry? I have a good sense of direction but will be doing it by public transportation...please let me know and thank you in advance....

If you are stayiing in Playa it is MUCH easier to get to Cozumen then to Isla Mujeres.
Just take a ferry over to Cozumel. You can rent scooters there and explore the island.,

We enjoyed the ruins of Ek Balám MUCH more than Chichén Itzá; the ruins of Tulum (gorgeous setting) and Cobá (very jungly and the big temple there is huge compared to the large temple at Chichén Itzá plus you can climb it unlike at Chichén Itzá) are closer and easily reached using colectivos or buses. We loved snorkeling with sea turtles at Akumal (no cost). We've made 2 trips to the area in the last 8 months and my photos, blogs, and travelogues are below. Happy trails!
http://www.flickr.com/photos/staceyholeman/collections

Where are you staying? we are going May 16th at Now Jade Cancun

Thank you for the responses. @ Nancydear...I am at the Playa Mayan RCI hotel, unsure exactly where. schmerl---- so it is out of reach for us to get to Isla Mujueres by public transport? Thanks again to all.

In order to get to Isla Mujeres from Playa del Carmen, you'll need transportation to get from Playa to the ferry station in Cancun.(about an 45 minutes to an hour drive) Then take the ferry over to Isla Mujeres. In Playa their ferry goes to Cozumel.

We've been to Mexico several times over the past 10 years and we are not adventurous enough to take collectives to get to attractions. We take tours with transporation included or taxis.

Thank you KVR.