[ZeikJT]

In 1996 when it was a proposed idea the estimated cost was 500 million USD and the proposed launch was 2007. But the design kept getting more and more lofty and the project got more and more complex. The initial estimate was a bit off, it has cost about 9.6 billion USD so far.

Still though, if everything works and we learn more about the universe, I think it'll have been worth it.