i don't think there's a single gym near me (with the exception of the university of course) which is less than 30/40 a month.
Although of course i wouldn't join a gym which doesn't at least have a swimming pool, but i can't think of any nearby which don't have a pool anyway.
Err, you're right that a 20 quid set of dumbbells won't keep you going for long, but another 20 kilos for about £20 (so 40 overall) will get you a set of dumbells around 20kg each, which with correct exercises will get anyone to an above average size (i know very few people that can curl more than 20kg per arm for example, let along do a tricep extension or a "dumbell fly"). Maybe 1 in 10 at a push when you consider most people don't go to the gym).
Anyway i know a few people that are pretty strong without the use of a gym, but of course there's no point naming them as you won't have a clue who i'm talking about.