Someone else has just started another thread about costs...
Re club membership, I don't think this is ever mandatory for legal reasons. With a Public CofA plane, anybody can rent it (subject to ratings, diff training, insurance etc). With a private CofA plane, only shareholders can fly it and each shareholder must have 5% of more (i.e. 20 max). I have a plane which I can rent out freely and, when it was insured for that, there was no "club" requirement.
I vaguely recall there is a rather odd CAA requirement in that flying events (e.g. club flyouts) may be advertised only on a club noticeboard...
Obviously a school wants you to join because they get some £50/year that way, for each person who does or doesn't ever turn up.