Book your flight in advance to save a lot of money.
I booked my flight tickets almost a month in advance and this is what I paid.
Round trip : 9,727 INR per person
Cochin (COK) – Bangkok (DMK)
Bangkok (DMK) – Cochin (COK)
Use Google Flights to find the dates with cheapest air fares. So you can choose round trip and then select the dates with cheapest airfare.
( You can decide the onward and return dates based on the price )
Double check the Airport names, dates and airline name.
Once you find the cheapest flight, try to book the same using websites like PayTM where the fare will be the same, but you’ll have coupon codes and cashback which will further reduce the total expense.