My boyfriend Wiebe and I travelled across Sri Lanka for 16 days and spent less than €500 p.p. for the entire trip. Sri Lanka is a cheap destination, however, the breakdown in this post is geared towards a budget traveler. All costs mentioned below are per person per day, but based on two people travelling together. It includes all expenses in the country itself, i.e. excluding international flights or insurance.
Crossing Sri Lanka with the train is very easy and inexpensive and a great way to interact with locals. The train ride between Nuwara Eliya and Elle was one of our favorite experiences from the entire journey through the country. The ride through the tea plantages in the Central Highlights of Sri Lanka is probably the most scenic rail journey you will ever take in your life.