How to book:

You can get tickets from the ticket booths at the city train stations - which is the cheapest way to buy one. However, Ho Chi Minh City - Nha Trang is a popular train route so sometimes it might be difficult to get the ticket as you arrive. The way to go around it is to reserve your ticket online. Ticket agents will charge you a commission when you reserve online - and the fee usually include tax and ticket delivery to your hotel in Ho Chi Minh City (such as Vietnam-trains.com). 

Ticket fare: $27 (Soft Seat)  - $36 (Hard berth) - $39 (Soft berth)