I took this shore excursion with my family while on a Holland America ship and it was well worth the money. It would be very difficult to do on your own because first we had to take a ferry boat from Cozumel to the mainland and then a bus to Tulum. There didn't seem to be any other way to get there.
The ruins at Tulum are fascinating and it is definitely a Kodak moment as the ruins are right on the water. In fact, if you go during the summer, you have time to jump in the water to cool off.
The shore excursion included a rest room stop in a nice clean store and an excellent, fresh, boxed lunch from Subway. At Tulum itself, there are souvenir stores and restrooms. It is a 10 minute walk from the parking lot to the ruins, but there is a little tram available for a slight extra charge.