Travel Portal - Zuji, Priceline

I enter "Budget Airlines" in Google Search and found the ad by Priceline.

I tested it for my trip to Brussels. It gave the same best deal (ie the same price) from British Air.

Two other airlines also advertise their special offers. I checked on the European airline, as they cover Brussels. Their best price is 50% higher than British Air.

Conclusion: It is better to try a portal, such as Zuji or Priceline. They can give the best deal. You can approach your favourite airline directly and see if they can match.