Santander Airport is located in the municipality of Camargo. Alsa links Santander Airport to different locations in the north of Spain including Bilbao. Buses stop at the airport provided that travellers have bought tickets in advance. For make a reservation with Alsa, please visit the link. There are about 80km, it takes 1h30min. and the ticket is about €7.
The airport web pages give detailed information about flights, airlines, directions and transport. The airport is located in the municipality of Hondarribia. There are several busses to San Sebastián (price €1.65), then from here to Bilbao there are many options.
Avda. Abandoibarra, 4
48011 Bilbao, Spain