A Club within a Club

I recently stayed on a CC site paying nearly £30 for my 2 night stay.  A price I considered fair for the facilities available.  At the same time I was on the site there was a CC Rally of approximately 20 caravans who had only paid £8+ per night regardless of how many people in each caravan (its amazing what you find out at the dish washing area).  As they had access to all the same facilities that I did could someone please explain to me why they were being charged much less than all the other members on site ( a loss to the CC of at least £14+ per caravan for the 2 night rally: times 20 caravans = approx £280).  Is there a Club within a Club?  Surely all members should be treated and charged equally?