Here's a great Planet Money podcast that features this movie! Basically the producer, Jason Blum makes money by highly restricting the budget for each movie. (he made Paranormal Activity for $15K)
Blum has very strict rules for his movies
Not too many speaking parts, speaking extras are on a different pay scale than non-speaking (also explains the empty extra less scenes, sounds like he limited non-speaking roles too).
Not too many locations, most economical is in one house
Pay talent as little as possible, pay using box office bonuses
Here are the two reporters discussing how "The Boy Next Door" follows those rules
Also there's nearly zero budget for special effects. They talk about the eye stabbing scene in the episode and I HIGHLY recommend listening (I won't spoil it) on how they had to make it work since they basically ran out of money and the scene wasn't going to be shot and the producer refused to give them more money to finish it.
Transcript: http://www.npr.org/t...oryId=439632877
Episode: http://www.npr.org/s...ng-in-hollywood