how much does a business man earn?
You can't answer. Its too variable. Barristers are self-employed, not salaried, they earn what they get paid by their clients.
I would think 40k would be the minimum for a practicing barrister, you would have to be reasonably good to get a tenancy, you can get this during a pupillage at a decent chambers. But it would go up and up and up if you were exceptional.