The answer to your question cam is they don't. They just buy a plane and do it. Or they're rich and can afford it. Or uncles cousins mama twice removed had an old one.
I totally agree with the post but I think vitalstatistix has a valid point. Day to day bus drivers probably do face a higher safety threat out of their control.
Trust me: dealing with ATC and other traffic in the air is much worse than people on the road. It's just that pilots are better trained, so it would be safer. The average airline of pilot has done thousands of hours.
http://funsubstance.com/fun/187269/-hail-to-the-bus-driver-/