Amtrak from NYC to DC fluctuates in pricing but can be $35 each way, if booked booked far enough in advance. That’s about the same distance from Rancho Cucamonga to Las Vegas. So I think it’s a similar ballpark to a plane ticket.
Flat pricing + make ticket good for something like 2 weeks to ride whenever.
If there was such predictability and flexibility, they'd immediately significantly increase their ridership.
There's a dead reply below that says "shinkansen are cheaper when bought in advance" --- I was led to believe otherwise, good to know as I ride it a few times a year.
Compared to trains being run as a semi government provided utility, like the Netherlands, where pricing is flat based only on route. Makes the train a more relevant alternative, which helps with road congestion. But tax money is used to build railways and stations, the tickets only pay for operating the train itself.
This can only possibly work with low ridership numbers. Imagine getting to the railway station with your bags and all seats are spoken for.