Just got back from walking the Camino Frances and was able to manage quite well with T-mobile (US customer) which offers unlimited data for T-mobile customers in Spain and the other European countries I visited. They supposedly "throttle" the speed, but I rarely had issues and was able to use...
This site is run by Ivar at in Santiago de Compostela.
This site participates in the Amazon Affiliate program, designed to provide a means for Ivar to earn fees by linking to Amazon