The Wikipedia entry on money shot indicates that the phrase originated in the film industry in general, not just in pornographic films.
Originally, in general film-making usage, the "money shot" was simply the scene that cost the most money to produce.
By contrast, Collins indicates it originated in the porn industry. To be fair, that entry only talks about the pornographic meaning of "money shot".
Where did it come from? Did it exist before the porn meaning arose? Did the porn industry take an obscure term and make it more popular?
Best Answer
According to the The Concise New Partridge Dictionary of Slang and Unconventional English it is a new AmE expression which probably originated in the pornographic industry in the late '50s.
Also the following extract from the The New York Magazine appears to suggest that the origin is from the pornographic industry: