Have you thought of using Bilbao airport ? It's a 1 hour 50 minute drive to h2o, same as from Bordeaux.
From there you can :
- hire a car* or take a Blabla car for about 15 euros
- or take a bus to Bayonne (Baiona) http://www.lurraldebus.eus/es/ (basque and spanish) Takes about 2 hours.
Flights to Bilbao from :
London Heathrow, Stanstead, Gatwick, Birmingham, Southampton, Manchester, Edinburgh, Dubln, Amsterdam, Brussels, Berlin, Dusseldorf, Franckfort, Stuttgart, Munich, Zurich,¨Paris Orly and Charles de Gaulle, Geneva, Milan, Venice,
* non-european drivers please note that you need an international driving licence to rent in Spain.