I think they're mostly travelling from Sheffield...
In which case, those close to the Sheffield > Manc railway might be ideal.
There's plenty of choice, the only other two along there I've used were Chinley, which might be a longish walk from the station, I had a bike, I don't remember the site, just the constant rain... And Whaley Bridge, train to New Mills and bus, followed by a long uphill walk to the site, cheap and basic, but not many level pitches.
I know a few more a bit further South, but not easily doable on public transport.