'Got to agree with the previous one.
I'm in 2 groups - a permit 2 seater and a Private cat. 2+2, both taildraggers & at different fields. Flying costs £20-£25 an hour + a share of fixed hangarage, insurance etc (about £800 for the two). Theres always at least one available, there both nice to fly and practical tourers (I've been over the Alps in both).
Check out the club noticeboards at your local fields and the ads in Pop. Flying, Flyer, Pilot etc..
One tip, a busy, active group is better than a sleeping group as their more likely to keep everything clean ,serviceable and in good condition.
Not really a downside, in my opinion, but expect to spend a bit more time getting involved with paperwork, 50 Hr checks and so on.
Insurers are usually happy if you get a thorough check out/ conversion.