I had to travel by Amtrak (forced, I lost my passport and I couldn't board a plane) from LA to NYC via Chicago once. ($230)

Not only I got to see a lot of places, but I truly accomplished more quality work than I normally do in a similar time-frame. Nearly zero distractions other than the occasional beautiful sight and the rest breaks I took, I had the chance to visit the surroundings of the major stations the train stopped at.

Perhaps it's my ability to sleep in the weirdest places, but I found the sightseer lounge car couches very comfortable. I went to bed 1hr or so after dusk, and I woke up with the morning lights. That's about 8h of sleep or so every night.

PS: Make sure to download a metric shitton of music before you do this. The sightseer car (the only place where one can truly work comfortably in the train) is usually a noisy place.