We do wild from time to time, but in the main we use Caravan & Motorhome Club CL sites. When you join you receive a thick publication which lists all their club sites (horrid large crowded and expensive) affiliate sites (professionally run large yuk sites) but best of all their 1,000's of amazing CL sites. These sites vary enormously in price from as low as £3 per night right up to super luxurious ones (which we don't go to) costing as much as £27 per night.
I usually sit down with my lap top keyed into their (dreadful) website and with the guide book in hand I go through every single CL listed that costs £12 or less that have good to excellent reviews........... we have discovered 100's and we always go for those that are very rural, no showers or loos, a large area of ground and with difficult access, the last point being that it normally keeps away travelling gin palaces and caravans!
ps. Also, if we are going spring to high summer when we don't need electric hook up and they offer it into the price, I always ask for a discount off the site fee if we don't hook up and normally receive a £2 to £3 discount, tight git that I am!