I'm not kidding when I say that you would be surprised at the size of the market for canned air. I made this same joke several years ago and then looked into it and was blown away.
You're not paying for the air. You're paying for the pressure differential.
That typically isn't air (80% Nitrogen 20% Oxygen) but a liquefied compressed gas such as 1,1,1,2-tetrafluoroethane. They're very handy for cleaning things, especially computer heat sinks. Much more portable and cheaper than an air compressor.