One of the reasons that campsites are more expensive here in comparison to the continent is really simple. Lack of competition from places to park outwith the campsites. In the continent there are tens of thousands of aires that are free or extremely cheap, the campsites in these countries have to compete. Another reason is there are more caravans here who guarantee business for the campsites, meaning that we are not as important to the campsites as we are in the continent. Another reason for cheaper prices is most campsites in the continent are municipal, not run for profit.
Providing more free or cheap Aires, combined with higher sales of motorhomes will bring down prices in campsites. But until attitudes change here, we will always have the most expensive campsites.