Short answer: IndiGo is most often the cheapest carrier on the Colombo (CMB) → Chennai (MAA) route, though Air India and sometimes SriLankan/other carriers can match or undercut it depending on dates and sales. (flightroutes.com)

Why: direct services on this short route are offered by IndiGo, Air India and SriLankan Airlines, and airfare on budget/low‑cost carriers (IndiGo) usually shows the lowest fares in searches/OTAs. (flightroutes.com)

Practical tip: fares change a lot by travel date, time of day, how far in advance you book and whether there are sales. For an exact cheapest fare for your dates, compare Google Flights/Skyscanner/Cheapflights and the airlines’ own sites (IndiGo, Air India, SriLankan). (skyscanner.com)

If you want, tell me exact travel dates and I’ll look up current cheapest fares.