Hi Mc Seans,
Welcome to the forum.
I was planning doing from SanSebastian to Santander next year, but then the longing to go over the Pyrenees at least once in my life took over. I would love to hear how you get on.
Aerlingus have fabulous value on their flights to Bilbao at present if you can make a definite date.
I am coming back from Bilbao on May 28th and my flight including tax, booked seat, rucksack in hold all comes to only €55.90
Buen Camino to you both
Lydia