A single NY-LA route alone would cost over $500 billion. High speed rail is well $100m/mile, just for the track.
All that said, of course, figuring out how to lower costs safely would be a great thing.
That's frankly an insane figure, and depends vastly on what you're building and where. For something that's largely running through rural landscape, you really should expect no more than half that for the total construction cost. Maybe US construction is that expensive, but… wow.
In France the average cost is €15m/km, and that's for extremely high standards / constraints (350km/h or 220mph nominal speed, incl. barriers & bridges for wildlife)