Short answer — fly low-cost or into nearby Sharjah and be date‑flexible.

What’s usually cheapest

• Air Arabia (direct CMB→SHJ) is often the lowest‑fare option — roundtrips from Colombo to Sharjah can show from roughly US$170–$300 and one‑ways from about US$150 in recent searches. (Wego.com)
• Direct low‑cost flights (Flydubai, Air Arabia) or one‑stop itineraries via regional hubs (Doha, Muscat) tend to beat full‑service carriers on price. Google Flights/Kayak show cheap round trips CMB→DXB in the ~$270–$450 range depending on dates/airline. (google.com)

Practical tips to get the cheapest fare

1. Be flexible with dates: midweek departures, off‑peak hours and shoulder season reduce fares. Use the calendar view on Google Flights/Skyscanner. (google.com)
2. Consider flying into Sharjah (SHJ) instead of Dubai (DXB). It’s a short bus/taxi transfer to Dubai and often cheaper on Air Arabia. Check total transfer cost/time before booking. (us.Trip.com)
3. Search multiple engines (Google Flights, Skyscanner, Kayak, Trip.com) and set price alerts — fares change frequently. (google.com)
4. Travel light: low‑cost carriers add fees for checked bags and seat selection; base fares are cheapest with only carry‑on. (Wego.com)
5. Book early but watch price trends: start tracking fares months ahead and buy when you see a dip or an alert. Tools like Google Flights and Hopper can recommend timing. (google.com)
6. Consider one‑stop itineraries (Doha/Abu Dhabi/Muscat) if direct fares are high — sometimes slightly longer travel saves money. (google.com)

Quick action steps (5–10 minutes)

• Open Google Flights and search CMB → DXB and CMB → SHJ using “±3 days” or “flexible dates.” (google.com)
• Set price alerts on 2 sites (Google Flights + Skyscanner). (investopedia.com)
• Compare total door‑to‑door cost (flight + baggage + airport transfer to Dubai) before booking.

If you want, tell me: 1) exact travel dates or a date range, and 2) whether you prefer lowest up‑front price (accepting fees and transfer) or shortest/most comfortable trip — I can search current fares and show cheapest options with links and total costs.