Zachary, the Matrix website is a favorite of mine, and others here, for searching airfares: http://matrix.itasoftware.com/

I flew from Charleroi to UK for less than 50 € one way.

When I book with aeroplan points, I pay taxes and airport fees, and some airports are definitely more expensive than others. For me, it would be helpful to know which airports are cheaper, although it seems that it's mainly flights to UK that are available when I fly business class from Vancouver, unfortunately.

Thanks everyone for the tips!

Just to be clear the tax for HIV is used to contribute to help children born with HIV especially

Still seems a strange idea. You pay for the total service to get you to where you want to go. Treating Europe as a one stop pick an airport is just crazy. I might want to go to Paris but I'm not keen on Crimea, so why would the relative airport costs be relevant. In addition since nearly all the costs are negotiable (except taxes) it would depend on airline.

Famously Ryanair makes the local Mayor pay for the opoortunity to have the airline base there for 40 minutes three times a week.

We do have cheap airports in Europe, often former military airports in the middle of nowhere.

Usually it is not the case that Ryanair pays fees for landing at these airports. The opposite is true: the airports subsidize Ryanair.

However, most of these tiny airports only have holiday traffic and no intercontinental flights. They simply do not have the infrastructure for transatlantic flights.

Is is cost-efficient to fly into these budget airports?

Often, the costs of transport to and from the cheapo airports eat up what you have saved on the ticket price. And the most expensive thing when travelling is time. Simply add all your costs for travelling - airfare, ground transportation, accomodation, food etc. - and divide the sum by the daylight hours of your whole trip and you get the cost for each usable hour.

And then you will think twice whether it is worth to fly into a remote airport and lose several hours for travelling to and from this airport.

It mainly depends on where you would like to fly. But I would say cheapest are Hungary and Poland

Don't forget that those "out of the way" airports are very convenient for those who live locally to them, or who want to travel to that area.

We have friends who regularly travel from East Midlands Airport in England (it's near Derby) to Carcasonne in France, near where they have a holiday home. It's not a journey that an American tourist would think of, but it's good for them, and profitable for the airline.

"Don't forget that those "out of the way" airports are very convenient for those who live locally to them..."

I've also used East Midlands, to go to Malaga with a friend who lives south of Birmingham. They are, as you say, good for those who live fairly locally and can take advantage of the very cheap flights, but public transport isn't the best so less useful (& less known) to visitors, even those staying in the area.