If you don't like the whole cancun scene (neither do I) a possibility is:

Take a bus from the airport to playa del carmen, which is 45 min or so south. Will cost roughly $2 I believe.

You can get a nice enough local hotel near the beach in playa for under $30.

Either hang out in playa or take the ferry over to cozumel and do some snorkling or something for a day.