The Space Elevator will never happen : LIGHTNING : both the 400,000V potential difference(average flow 1800A worldwide)and the Debye effect(reactive ions in orbit). If there is even a HINT that these science fair teeny boppers will short out that spherical capacitor and drastically change our biosphere(no 50V/meter electropotential gradient)with their elevator cable, the cuffs will be on them pronto........Yes, one pound to LEO runs about $20,000 on the shuttle. The actual energy value(mv^2/2 + mgh)of one pound in LEO is 4 KWH, or about 40 cents @ 10 cents/KWH. Arthur Clarke began to expound on that during an Apollo launch when Jules Bergman(remember him?)cut him off like a meat cleaver, NASA doesn't want you know how BIG their markup is : $20,000 for 40 cents worth of work......Thus it was that in the 1980's, during the salad days for SDI, a small slice of the aerospace community proposed EMSL : ElectroMagnetic Space Launch : shooting artillery projectiles into LEO at some 10% efficiency($4/#). The best idea, in my opinion, was the quenched superconducting ring-cannon(about 300 ft long to achieve 5 mps injection velocity). The studies were quite extensive, it looked very feasible, but nasa squelched it : it was too good of an idea which meant the ROCKET SCIENTISTS might have been out of a job. It's called VESTED INTERESTS, and no VESTED INTEREST ever funds its competitor...
By my calculations 5 miles a sec in 300 feet means an acceleration of 36000 G's. Sounds like you need a much longer tube if your not going to crush your payload into a pandcake!
Except for the little matter of acceleration and what it does to the delicate payload (e.g., astronauts). Anything but pig iron is probably too fragile to launch. That and Congressmen.
--Boris