Most flight search engines will only provide a search for scheduled flights, leaving you to look and compare the budget airlines yourself.
Skyscanner searches both scheduled and budget airlines (such as Ryanair and AirAsia.) The price of the budget fares takes into account compulsory fees such as taxes and airport charges, but you will need to add baggage fees. Skyscanner also lets you compare prices in a selection of currencies and you can book from any country in the world.