|NIST carbon nanotubes for sale|
At least, that's the current cost of the carbon nanotubes, if you want ones free of impurities. NIST has started selling single-walled carbon nanotubes, certified to be free of certain contaminants: $865 for 250 mg of the stuff.
That's 61 times the price of gold, per ounce.
As I wrote in my recent Physics World article, a carbon nanotube is the only existing material that is both strong enough and light enough to satisfy the demanding engineering requirements of a space elevator. (Basically, you need a material that can hold up about ten thousand kilometers of itself without breaking.) It remains to be discovered how to combine something that basically looks like a pile of soot into something durable like you'd need for a space elevator ribbon, but let's assume the SmartPeople (maybe these guys) work that out. What's the price of just the CNTs?
Well, the mass of the elevator will depend on its length (which, in turn, depends on how much of a counterweight you can manage to attach its space-end), and on its shape (which would be some kind of taper, widest at geosynchronous orbit). You can play with these (and here is a great spreadsheet by Maurice Franklin that lets you do just that), but the length is likely to be about 100,000 km, and the GEO-to-end taper ratio about 2-4, so the mass is going to be somewhere around 105 kg.
At the NIST list price that will run you about $350 billion, or 0.5% of world GDP. Pricey even for Google.
Of course, this is just NIST's introductory price for uncontaminated CNTs -- it will likely drop by the time the elevator ribbon construction facility gets going.
And NIST will surely give you a big discount if you show up with a checkbook and say you want to buy in bulk.