Somewhere between 40 and 100 USD depending on location.

But as wages increase and the market is able to bear higher prices, its unlikely to increase to those prices, since the rail network isn't run for profit.

Prices will still go up as labor costs increase, just not as much as they could, similar to rent and food.

There are of course far cheaper options such as hard sleepers, soft seats, and hard seats, which pack 6 beds per birth, 8 seats, or ~12 seats respectively, and also a more expensive option on some trains that's 2 beds per berth.