China built a national high-speed rail system for less than how much our bipartisan infrastructure bill cost. This means that we could have all lines connecting basically any pair of cities <500 miles apart if we were as efficient as China, for less than $1.2 trillion. This includes earthquake zones and mountains in central China (ie Kunming to Shanghai 190 mph is mostly tunneled and actually was cheaper than most of the other lines).
This entails a Chinese approach to private property, which I have no interest in. Surely we can cut costs without adopting quasi-communist despotism.
I would just pay everyone 10x what their land is worth in rural areas (surely this will get almost everyone to move), since their land isn't worth that much anyway (as compared to the suburbs/urban areas), and try to tunnel under the suburbs or build the rest adjacent to highways. In the worst case, I would use existing lines (though the problem is that Amtrak doesn't own them, freight companies do).
I would also use the Chinese approach to cheap labor and environment: hire people from foreign countries where our minimum wage is a good wage for them, and give them temporary visas until the construction is complete. Cut the environmental review process from several years to 6 months at most.