http://www.hendra-holidays.com/index.php
or more specifically:
http://www.hendra-holidays.com/bookings/holywell.aspx
A H3 caravan will sleep 6 comfortably (2 x doubles, 4 x singles) or 7 if there are a Mr & Mrs (or two open minded Mr.'s!) and costs £385 for 3 nights (Fri - Sun), which works out at £65 per person for the duration.
Alternatively there is camping also on site, at about £10 pppn (though working out their tariff structure isn't the easiest thing in the world!!

Probably about a 25 min walk to the venue from there.