third, who are you to decide what is fair? you didn't write the app, and have no idea how much time, effort, and resources went into the development. if it took me 3 man years of development, and i had to pay to license some technology, and i decide it needs to cost $30 for me to recoup my losses and make a small profit, who are you to tell me different?
I am the only one with access to the necessary data to decide what value I attain from the use of the software.
It doesn't matter how much it cost you to provide, if you can't provide it at a price that matches the value it gives to me then it costs too much.
In your example, if you need to charge $30 to make money and I don't get $30 of value from the use of your software, then you're the one that fucked up, not me.