Cheap horror films are one of the few exceptions to the "multiply the budget by 3x and compare to the box office total to see if it was profitable" rule of thumb.
Look at Dark Skies back in February. It cost $3.5M to make and took in $17M total at the domestic box office. On paper that looks good, but the marketing and distribution costs would have been several times more than the $3.5M production costs.
The film opened wide in 2300 theatres, so those extra costs would have at least been $10M. For instance prints cost $1500-2000 per screen that a movie is playing on. Assuming that 2300 prints were needed (ignoring the fact that the movie would have played on more than one screen in some venues), that's $3.5-4.6M just to get the film into theatres. Now add in the cost of internet/television/print market, movie posters, trailers etc. Even for a modest ad campaign it ads up. As such, Dark Skies probably didn't turn a profit in theatres despite the tiny budget. DVD sales and TV licensing will probably rectify that at some point though.
