Ángel Albino Corzo International Airport (TGZ) is located 30km outside of the city. There are currently direct flights to Mexico City, Cancun, Monterrey, and Guadalajara. A taxi to downtown Tuxtla costs $20. Taxi companies have to pay fees to the Federal Government to operate in the 'Federal Zone' of the airport, as in most countries all over the world. Fares departing the airport will reflect that. You will have to buy a ticket for the taxi in the airport. Though colectivos do not come up to the airport itself, they pass by it on a road a short walk from the parking lot and cost considerably less than a taxi as they are not within the Federal Zone.
There are direct buses from Angel Albino Corzo airport to San Cristobal de las Casas. Times and prices can be found on the [url=http://www.ticketbus.com.mx/wtbkd/index.jsp]TicketBus[/url] website. As of May 2011, the price was 160 pesos and buses left early and mid afternoon, taking about an hour.
There is a modern OCC terminal that can be reached by Colectivo (Ruta 35) - ask the driver to stop. From there you can arrange onward travel to most destinations in South Mexico. If you are heading to Oaxaco, it is around 10 hours and costs around M$500, you could always break the journey at [wiki=9a3837ccdd0a56bc0d5a9890649bdabb]Juchitán de Zaragoza[/wiki] (5h - M$222.00).