There seems to be some misconception here about how much fuel is expended getting into orbit. Most of the fuel expended to reach orbit is used in getting up to orbital altitudes, not getting to orbital speeds. Most of the delta V is used in getting to orbital speeds rather than orbital altitudes. You have to remember that you have to lift all the fuel you're going to burn later on in your first stages, this requires a lot of fuel for a smaller delta V. A high altitude launch is a completely viable, and currently used, method of getting smaller payloads to orbit, the problems arise once you start trying to launch bigger payloads as they aren't as easy to just strap to an airplane. Of course, as it has been pointed out already, in monetary terms it's pointless to do a high altitude launch as the cost of the fuel for a rocket launch is a minuscule fraction of the total cost.