I was thinking about a aircraft launched rocket - not the crazy balloon idea.
You can carry an (empty) space shuttle on the back of an airliner.
The pegasus is a pretty successful system - I was at the launch of an Infrared observatory by it 10years ago.
According to their site they can put 450kg into LEO, only about 1/10 of the capacity of a Delta or Ariane but a lot cheaper!
You probably aren't going to use it for a GSO communcations sat but great for GPS, sat-phone etc in LEO, especially because you are so flexible in the orbit window.
They claim the biggest cost advantage is that they don't need a steerable rocket motor.
To control a rocket's attitude at launch you need a lot of torque to overcome any wind or imbalance, that means a seriously complex vectorable rocket motor.
The pegasus can make much more gentle course corrections with just aerodynamics.
i suppose this is just because they have much more time and space to play with to make corrections because there is nothing around them.