As someone from Russia, we have even larger territory, and going by rail is almost twice as cheap as by plane.

High speed rail from Saint Petersburg to Moscow will cost you ~$45, going by plane will set you back ~$75 on the cheapest flight with hand luggage only.

Same story with long distance trips - I plan on going for a 1000km trip in July, and train ticket costed me the same $45, while cheapest plane tickets go around $100. It’s also a night train with beds and all, so I have one night accommodation for free while on my way. Depart - have a nice sleep - be on your destination.