Camp sites in Spain aren't as expensive as the urban mythologists claim - it's just that there are hardly any municipal sites so there is not a like for like comparison on that score.
Generally 2nd class category sites cost about €12-15 per night for a lone biker, and about €3-4 extra for the pillion. This is away from the coasts and big attractions like the Ordesa National Park. In contrast to France, however, these site have fill bar/restarant facilities that are open until midnight. You certainly won't be ripped-off in a spanisg camp site, where a 25 cl  costs from €1.20 - 1.50 - unlike in France, where I found myself paying €3.50 for a Kronenbourg last week!
It's always best to look for the secondary roads, but epecially at this time of year. Check out some of my Pyrenean routes for a few ideas.
Simon
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