We're going to start charging for oxygen. $100 a breath. Since you want to live and all you'll be willing to pay so it's not too much!
We are charged for air already try felling your tires at a gas station sometime.
The air is free, you pay to use the compressor.
Actually you are not paying for the air. You are paying for the use of the equipment and electricity it takes to pump that air. But their profit is still 99.9% of that cost.