It's a Freemium game. There is an option to buy 'BUX' but I haven't had to do it once or even really thought about doing it. They make it very easy to get coin/bux so I don't see a point. Maybe as you get further into the game? But even then you will have more planes and airports to make more money.
I haven't got anything done today at work. My boss even came by my office and said every time he walked by I had my head down looking at my phone.
