The 5000th doesn't help the person who paid for the first one. That would be the State of California in this case. Unless Mr. Musk would be willing to sign a contract for expected-10th-implementation-cost and not a dollar more?

It's pretty common to amortize R&D costs over future expected sales.

So who will be the first to offer a signed contract to build the SF-LA line for $6,000,000,000.00? Maybe A16Z will be interested in providing venture funding.

As others have pointed out, 6bn is about the cost of the Bay Bridge extension or, if you prefer, six Instagrams or other retarded "tech" startups.

This is not aimed at you, but when I started reading Hacker News I was amazed how excited, interesting and smart people were on this site. But now Im starting to get tired of this 'valley think'. Greetings from Switzerland where mind blowing infrastructure projects are still happening. http://en.wikipedia.org/wiki/Gotthard_Base_Tunnel

In case it wasn't clear, I was voicing my doubt that any company would actually build such a line for $6B claimed by Musk, not an opinion that it was unduly expensive.

Infrastructure projects like this a usually not financed by companies. The I-5 wasn't either.

And that was a poke at Silly Valley's tendency to see private funding and companies as solution to all of its woes (Sidecar, Avego, et al) ;)