Parish councillors don't get any allowances unless they are chairs. Borough councillors in most areas get expenses, and receive more if they chair a committee.
If you do the work properly, it is a full time job and then some. Considering doing it for the money is not a good idea at all. Our local borough councillors get £11k pa, and an extra £6k if they chair a committee, which will often mean meetings all over the country and meetings until very late at night.
The system is cheap. Making these positions proper "jobs", in my view, would discourage the right people from standing for office and attract career politicians, which are a total disaster.
And anyone can stand. Our local parish councillors range from people who run the local greasy spoon to a young man who works in community liaison (there's only one "wealthy" councillor). Our borough councillors are publicans, ex-NHS workers, former SATH mums, an ex-taxi driver, someone who works in IT support... it's a real mixed bag.
Anyone in a top job would not have the time or flexibility to do the work or attend the meetings. And if people are very wealthy, they can't really be bothered with the commitment.
You have to be very civic-minded, and willing to put the work in for very little in return.