I suggest you take the basic entrance fee if you are not a big eater. You must know that the package that includes food counts only one meal which is an all you can eat buffet but only once in the entire day. There are packages that include bus, entrance and food but I took the public transportation to go (160 pesos return) which can end up much cheaper depending on the package you find. The food there is excellent and lots of choice! But that's not really what you go there for.
You must get there as soon as it opens 8:30 am if you want to have time to see and do everything. Start with the underground river. Really refreshing and cool! It is not worth snorkling. You will enjoy as much just seeing the above water scenery. Then you stop at the beach to have a drink or take a nap in a hamoc by the sea. The choral aquarium is a must to see, la Casa de Arte is amazing, the butterfly sanctuary, the Maya village (there is a show at 4 pm) and then the grand finale at 6 pm (depending on the season). An incredible voyage in time from the Mayas to the musical and colorful mariaches of today. There is too much to describe. You have to see it. It is worth the 80 $US.