"A lunar space elevator can possibly be built with currently available technology [kevlar cable] about 50,000 kilometers (31,000 miles) long extending through the Earth-Moon L1 point from an anchor point near the center of the visible part of Earth's moon" http://en.wikipedia.org/wiki/Lunar_space_elevator

Roughly 3000 metric tonnes of cable + equipment needed to be lifted to Lagrange point.

"Commercial geosynchronous launch prices per kilogram have fallen 34 percent between 1999 and 2008, said a study by Tauri Group. They dropped from an average of $32,000 per kg to an average of $21,000 per kg, said the study commissioned by Arianes pace"

3 million kg * $21,000/kg = 63 billion dollars

Non-rocket launch alternatives and economies of scale could reduce this significantly. One type of elevator was estimated to have a 6 - 20 billion dollar cost:
http://en.wikipedia.org/wiki/Space_elevator_economics

Now to the "why can't we have nice things" dept.

"Congressional Budget Office: Cost of war to exceed 2000 billion dollars"
http://www.informationclearinghouse....ticle15499.htm

Interesting but:

Location:

In these positions, the forces of gravity and centrifugal force are equal, and as long as the system remained balanced (L1 and L2 are in unstable equilibrium along the line between Earth and Moon), it would remain stationary.

Not impossible but difficult.

Grettings.