
A friend recently imported a dog of 20kg plus 10kg crate to Heathrow and the Cargo and associated charges were over £1000!
I flew back with My Inka (using American Airlines) in December for flat $150 per dog each way as excess baggage, but as said above flew back to Brussels and then hubby picked us up by car.
It was cheaper to pay for the Ferry/Tunnel and fuel than to go cargo, as I was flying anyway (my return flight was around £750.