Does any one know of any cheap less than �10 a night campsites near trainstations?

Me and my boyfriend are looking at going camping next weekend but are now stranded after being let down by friends so are looking for campsites that will accept back packers. We would like the coast and are looking at places near Barmouth and Bala as they are cheap to get to on the train. But any other suggestions are welcome. We just want a long weekend away camping