In reply to goldmember:
How about staying in the Bunk House at Waun Fawr, North Wales (Bach Adventures) it's about a tenner a night, lots of hills there to have a good time in, not far from some good locations like Beddgelert and Capel Curig (by car) I did some good walks around Moel Tryfan, Mynydd Mawr and the surrounding area, some nice nature reserves there too,
Plus the steam train as well.
http://www.bachventures.co.uk/accommodation/
Its basic but I had to good times there ... Expect it to be busy this time of year though
Jason