We stopped using Heathrow as a mid-way point to getting budget airfare to Madrid.
Heathrow's "taxes, fees, charges and surcharges" are now at $614.90 CAD for a return flight from North America. They were $500.00 when we stopped landing there. Ironically, Air Canada is offering flights right now for $97.00 each way, but when you add the fees there are essentially no savings. They're not filling those seats. Basically you're paying 615 bucks up front, and THEN you buy your ticket at whatever the market will bear.
Most other airports are not quite that high, but ridiculously high anyway. And by the way, this isn't an Air Canada charge, it's a Heathrow charge - other international airlines all list the same fees.It may vary by a few bucks depending on the price of your ticket, etc, but basically around $600. overall.
I would investigate other airports or just fly straight to Madrid (fees are around $480).
lynne