It is free
There is a self guided tour that you can get through your phone that gives information about the mission. Most parts are open for viewing. The state park offices are closed on site when we were there but there is still plenty to see.
The audio is available online. When you see the printed display, you will notice a number corresponding to one of the list of recordings. There are group tours for the Alamo, not sure any for the Missions.
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