That depends on many factors from the difficulty of the job to the type of film used. It is easy to do 50 sq ft on a window that measures 60" x 120" tall. That can be installed quickly vs the same 50 sq ft in 50 individual french panes. See my point. Also, a window size that allows you to do the install with very little waste is less expensive than one that maybe has 10" of cut off on every window. It is nearly impossible to just give flat sq. ft. price numbers without knowing more about the particular job. If you do it that way, you may get lucky and have some very profitable jobs, but you will also end up with some that you take it in the shorts on. Just my $.02.