Merida and a cenote

Hi, I've never been to the Yucatan before, so I'm really lloking forward to our cruise. We leave out of Houston on Saturday. I had planned to do excursions through the cruiseline, but money has become mroe of an object than I expected. So instead of paying $90+ dollars for an excursion before other costs are added on, so I would like to research other avenues. This is also my first cruise so I'm uncertain how I can realistically plan my time while in port.

I'd love to go snorkeling in a cenote. I know that Dzibilchaltun<sp> has one, but I'd really like one that's at least partially underground. This one south of Merida sounds good....

http://alanformstone.com/pics/kk_sabakha.html But should I take a tour or take a bus?

I've done some traveling in Mexico before and speak some Spanish, so the public transportation doesn's scare me while the prices for the excursion does lol. I'll probably bring some of the family with me if I can convince them so I wouldn't be winging it on my own.

Anyway, so is it possible to see Merida and the Kanchirixe(sp) cenote in the same day and still make it back to the ship before it leaves at 4? We arrive in Progreso at 8 and I plan to be ready to leave at the earliest possible time to make the most of our time in port.

So, what are some quick suggestions? I'm not married to the idea of the cenotes and like seeing ruins as well. The thing is I hate large tours with a passion and would rather avoid most crowds. Are there any good sites within easy reach of Progreso that are a little less travelled?

Thankss in advance!!!