Richard - have a look on the ACSI website - http://www.campingcard.co.uk/gb/en/europe/france/languedoc-roussillon/herault/ - they specialise in 'low season' campsites, offering a discount over the normal site prices, with bands of 10, 12, or 14 euros - and there are several sites around the Beziers area. I'm not sure what sort of site you're looking for, but at this time of year there'll be no need to book a site - just turn up and see if the sites suit you!
The two I mentioned above are Camping Cheque sites, also offering discounted site fees, at
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