My local U3A group U3AC in Cambridge is independent of all the others. Illness means I’ve not been a member for several years, but unless things have changed:
There are about 300 courses. Many happen once a week for three terms, others are one or two terms only, or once a month throughout the year. Anyone can join, the only stipulation is that you don’t also have a full-time job.
The annual fee is £120 this year. Most courses are run by volunteers and there is no extra charge for most of them. If they have an external tutor who they need to pay then there will be a charge, but this is clear in the course brochure. Anyone can volunteer to run any course they like - many of the tutors have been teachers or university lecturers, or just have an interest in something.
Initially you fill in a course preference form, where you can nominate up to 5 courses, with alternates. Some clever computer programme allocates as many as it can to their first choice, those who don’t get it have priority for their second choice, and so on until all the choices have been worked through. Any courses you’ve not been given you can go on the waiting list for, in case people drop out.
Courses with vacancies are then advertised, which you can signup for at any time. There are also weekly lectures, a film group (where the chosen films are shown at a local picture house) and so on.
The group hires rooms in meeting halls in various places all over the small city and also rents a property in the middle of centre for meetings. It has a social area with a self-service coffee machine for drinks etc (£1 each?) which anyone can use when the building is open.
One of my courses has stopped running after a few years, but the members still meet in a pub once or twice a term to discuss the same things. There were far more men than women in that group, but other classes have been mostly women: the sex balance seems to depend on the subject.
£120 sounds, and is, a lot of money. However, when I was last a member I was doing 3 different dance classes (all taught by retired dance teachers) and two craft groups a week, so it worked out at less than £1 a meeting.
Edit: here’s a link to the course brochure. I recommend it to anyone within easy travelling distance of Cambridge.