My understanding of the problems with high speed rail in the US is more fundamental than money.

The problem is loose vs strong property rights.

We don't have the political will in the US to use eminent domain like we did to build the interstates. High speed rail ultimately needs a straight path but if you can't make property acquisitions to build the straight rail path then this is all a non-starter in the US.

Just commission the Chinese and make it 10X bigger then. In the case of the AI, they appear to commission Sam Altman and Larry Ellison.

The US has tried to commission Japan for that before. Japan gave up because we wouldn't do anything they asked and went to Morocco.

It was France:

https://www.businessinsider.com/french-california-high-speed...

Doubly delicious since the French have a long and not very nice colonial history in North Africa, sowing long-lasting suspicion and grudges, and still found it easier to operate there.

It doesn't matter who you "commission" to do the actual work, most of the additional cost is in legal battles over rights of way and environmental impacts and other things that are independent of the construction work.