Alternate Reality Games

I found this interesting video publicizing the alternate reality game "The Pirates Society". Everything looks so real, mysterious and challenging. And adults got involved in this for weeks. I wonder how much people pay to get involved in those games? It must be really expensive, taking in account all the real things that need to be set up. All in the name of adventure and mystery, feeling you are part of a real film. I was thinking, in relation to interactive storytelling, how much of the sequence of events in the game can be changed, and even if the end of the game can be changed by participants or not.