Short answer: AirAsia is typically the cheapest carrier on the Colombo (CMB) → Kuala Lumpur (KUL) route, especially for nonstop flights. (trip.com)

Details and context (as of September 15, 2025):

• Aggregators show AirAsia offering the lowest nonstop fares (examples around USD $100–$125 one‑way / ~$245 round‑trip on sample dates). (trip.com)
• Malindo/Batik Air often runs low‑fare promos too (promo fares advertised from RM429 one‑way). (malindoair.com)
• Full‑service carriers (SriLankan, Malaysia Airlines) operate the route as well but are usually more expensive than the low‑cost carriers unless you need checked baggage or flexible tickets. (srilankan.com)

Tips to get the cheapest fare:

• Compare dates on Google Flights, Skyscanner or Trip.com and set price alerts.
• Check baggage/seat fees on low‑cost carriers (these can raise the total cost).
• If you want, tell me your travel dates and I’ll look up live fares and the cheapest options right now.