In reply to afx22:
Another vote for Dolgam, which this year has put it's prices up to £6/person/night. They have invested a lot in the site over the last couple of years to improve the facilities and add drainage to the most boggy areas, it has lost some of it's "character" but is still very much a walkers/climbers site with simple (spotlessly clean) facilities.
Only downside is that you will probably find yourself driving most days, but being slightly lower than those in the Ogwen valley it doesn't get (quite) as battered by the wind. The pub is walkable but just that bit further than you would like after a long day on the hills, which in itself could be seen as a bonus.
Post edited at 14:15