The answer is it depends. are you looking for budget stays then you should look out for deals on mmt or Airbnb. Travel costs won't be very high from India. For e.g. if you are travelling from Bangalore then one side tickets should be around 5-8k depending on how early you book. Visa on arrival is available for Indian citizens so that's not a concern. Plus the rupee is stronger there so things are not very expensive there. Happy travelling!
For visa you need to get ETAs done. They are valid for 30 days from the day you entered the country. Excluding the flight fares, if you are staying in Airbnbs then your cost can come up to Rs 20k-24k. Many Airbnbs don't include the breakfast, so if you eat outside, you can add another Rs 15k for food. One more thing, SAARC country visitors get a discount on most of the Government tickets like in Sirgiriya and Dambulla museums, Temple of Tooth relic, etc
Sri Lanka is a great place to visit! Do take Visa before hand. In around Rs2-3000, you get very good resorts and hotels in Colombo. Colombo is a mixture of Buddhist and Colonial Architecture..also a hub for casinos. Enjoy your stay!