In reply to RX-78:
I have a base membership at my wall that was £30 once and gives you a discount each time for a year, and I am getting a concession as a student. That way I pay £6.50 untimed, and £4 for one hour of climbing during weekday lunchtime hours. The latter sounds like a pretty bad deal, considering it's only one hour, but it saves money and if you boulder continuously you can get yourself pretty tired within just this one hour.
I go twice a week, once untimed, once lunchtime, so £11.50 a week, £46 a month. Comes out slightly cheaper than buying a 6 months membership, and costs more than annual membership, BUT I obviously don't climb while travelling, or on vacation, plus it's more flexible.