I went on one a few years back, I think it was about £100 for a weekend with overnight in a hostel type accommodation. It was run by the BTCV and was great fun...we drunk a bit to much dizzy juice in the evenings and learned how and when to lay hedges.
I had a bit of a head start because as a young lad I had helped my Dad and Grandad lay hedges, but it was good to learn the proper theory. and a great social weekend. Went on a dry stone walling one too by the same outfit. Again it was great fun.