Well, this looks like it would be a fab site for anyone, but they actively encourage people to go without a car.
The site is Graig Wen in Snowdonia http://www.graigwen.co.uk/tent-camping-fields-2.php
It's close to a train station and they offer a pick up/ drop off service. They look to have good facilities and the site says that the area is easy to get around without a car. They also have bike hire.
And if you go without a car it's half price
They charge per person and so it would be £4 a night per adult and £2 a night per child (weekdays) Bargain
Anyway, just thought I'd share this as it's not easy to find sites that cater so well for car-less people, nevermind sites this nice looking for so cheap.