It's not reasonable to expect rockets to run as cheaply as airplanes:

   Airplanes draw oxidizer from their environment; rockets must contain
   and lift their oxidizer.

   Few airplanes generate enough thrust to lift the airplane vertically;
   instead, wings allow a thrust less than the total weight of the
   vehicle to lift the aircraft over time. Wings don't work in vacuum.

   Airplanes draw air from their environment to accelerate backwards for
   thrust; rockets contain and lift all the mass they eject for thrust.

   If you want an airplane comparison, picture a Boeing 747 flying on
   afterburners that can lift it vertically, and fill the interior
   with LOX. Sounds like a rocket, doesn't it?

There's an astoundingly fantastic rocket primer at:

http://www.projectrho.com/rocket/index.html

It needs javascript for menus.

Brian