If you are going in the month of March 2019, you'll be able to get cheapest tickets for Iceland from Delhi. Early of this month I checked, the cost was under 40000 for return ticket.
The air-fares totally depends upon season for any travel destination across the world. Peak season is from June-September, so avoid going during these months. Ideal time for travelling to Iceland is from October-April. You can find great deals on air tickets here: https://www.skyscanner.co.in. Skyscanner is a global travel search engine that compares the prices of all major airlines. Have a memorable trip!