That will depend on many different factors, like the type of film used, accessibility of the windows, and size & shapes of the windows. Windows high up, may require the building of scaffolds, while French windows require the cutting of many small patterns. Most residential/commercial installations start at around $7 per square foot, but the price can change, depending on the differences stated above.
Residential comes with a lifetime warranty, while most commercial films come with a 10 year manufacturer’s warranty.