The most trusted & cheapest site for booking a flight is:

Firstly, you have to Book Direct Through The Airline’s Website or if you aren’t able to then you can take help from some travel agencies that provide the cheapest flight booking.

Skyscanner: Skyscanner scans 1,200 airlines and travel agencies and consistently produces top-notch results, especially on challenging itineraries where they frequently combine flights from two different airlines. At the airport, you might have to change airlines, but it's worthwhile if you want to save money. In that case, you can filter the outcomes to find the "fastest" path to take.

Momondo: I particularly appreciate that you can search for hotels, travel packages, activities, and car rentals in addition to flights and that you can exclude red-eye flights if necessary. Similar to a one-stop shop.

Traveljunctionus: Travel Junction is one of the greatest resources for finding low-cost flight prices. Because it makes use of the powerful ITA Matrix search engine, which was created for travel agents.

Orbitz: Search from a variety of hundreds of top suppliers who provide Orbitz users with the most extensive and exclusive range of holiday packages, flights, hotels, rental cars, and cruises.