In comparison with power it's pretty cheap to try - Stratford will give you a winch-launched trial lesson for £50, as will Shenington, and the others will launch you by aerotow for £75-£90.
Well that is about £500 per hour for a winch launch flight (average flight 6 mins) and about £ 360 per hour for an aerotow (average flight 15 mins) ....what you mean its pretty cheap??
Gliding Clubs who charge these outrageous prices for a genuine "trial lesson", rather than a jolly, and not going to get many new members.
UV