Short answer — use a price-aggregator + the airlines’ sites, and set alerts. Best places to check for Colombo (CMB) → Chennai (MAA):

• Google Flights — fastest way to scan calendars, compare timings and set price tracking. (google.com)
• Skyscanner — good for finding the cheapest month/days and comparing many OTAs at once. (skyscanner.net)
• KAYAK (or Momondo) — another solid metasearch that surfaces low-cost carriers and recent deal alerts. (kayak.com)
• Airline websites (SriLankan Airlines, Air India, IndiGo, FitsAir) — check them after you find a fare (sometimes they have the best promos / clearer baggage rules). (srilankan.com)
• OTAs like Expedia can be useful if you want price-tracking/protection or bundled deals. (expedia.com)

Quick tips to get the best deal

• Compare at least Google Flights + one metasearch (Skyscanner or KAYAK), then check the airline site before booking. (google.com)
• Set price alerts and track the route (Google Flights / Skyscanner / KAYAK all have tracking). (google.com)
• Be flexible on dates — midweek or flying in the cheapest month can cut fares notably. Skyscanner and KAYAK both show cheaper dates/months for this route. (skyscanner.net)
• Watch baggage and seat fees on low-cost carriers — the base fare can be low but add-ons raise the total. (Compare the full “total price” before booking.) (kayak.com)
• If you find a good price on an OTA, check the airline’s site before you pay — sometimes the airline will match or beat it and is easier for changes/claims. (srilankan.com)

Typical fares (recent examples)

• Metasearch results recently show one-way deals often around ~$90–$130 and round-trip low fares in the £90–£140 / $100–$180 ballpark depending on season and carrier. Prices move fast, so check live searches. (kayak.com)

If you’d like, I can:

• run a live search now for specific travel dates (and set up a short list of the cheapest options), or
• show step‑by‑step how to set a price alert on Google Flights or Skyscanner.

Which would you prefer?