HI Ive just done a week on the Norte (all that i could get off work) i was surprised at the scarcity of albergues compared to the french way portugese or even the via de la plata .
Having said that lots of holiday /hostel accomodation on coast between irun and Bilbao but obviously at a higher cost.
I suspect away from Bilbao things will get better /cheaper ,first week was surprisingly hard given elevation gains and surface , lots of stone and mud and weather made it worse lovely views and very nice people as ever.
I was travelling alone and normally dont book ahead however on a number of occasions i found myself with accomodation problems , without a booking , partly due to the time of year and national holidays etc , so suggest booking at least some accomodation in advance , if your going in a busy time of year or at the end of the season when a lot of albergues close.
Great route though cant wait to return.
Buen Camino