A space elevator is a very smart investment. Brad Edwards, a proponent of the space elevator concept
lists these figures in a space.com interview:
cost of space elevator: $10 billion
cost of proposed Millennium Tower envisioned for Hong Kong Harbor: $13.5 billion
cost of Gibraltar Bridge project: $20 billion
As Edwards says:
"I think those projects are a lot harder than what I'm talking about."
If investors can come together, it is a financially feasable project. The proposed elevator will initially
be able to launch multi-ton payloads every few days. If the space elevator can keep operation for any
length of time, it would be easy to recoup initial cost by charging to lift people and material into orbit.
Beyond that, there is a large economic incentive to research things like carbon nanotubes. They have so many
potential uses that an investment in them now can pay off down the line, space elevator or no.
Both the Liftport FAQ and Space.com's article have more information
of the proposed economics of this venture, however tentative they might be.