There are ports all along the North Spanish coast, offering everthing from fully serviced marinas in major ports through small local marinas to fishing villages with just moorings. Those in the first category include Santander, Bilbao, Gihon, Corunna. While they offer every facility and are well sheltered, being in busy working harbours they can be dirty and security may be an issue. You might consider somewhere a bit smaller with a good local marina - I would fancy somewhere like Ribadeo. Get hold of a copy of Robin Brandon 'South Biscay Pilot' for a good description of what's on offer.

The weather can be fairly wet and sometimes stormy in winter, so good shelter is important. The further west you go, the more attractive it gets, but transport connections get more difficult. Can't help you much on prices, but its a lot lower than the south coast of Spain, specially outside the main cities.