"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