IMO £4-6 is about right. When I take my son Adam with me I have to pay twice so £16-20 per night is expensive. Not that I will make it more than twice a year to this site due to distance, but for this type of camping I think £4-6 is fair.sounds good to me matey
I think about 8-10 quid per person per night is a good starting spot.
do you have a bit more detail on the local ie an area so we might look at transport links etc