The surplus revenue is public money because the Royals gave it to the Treasury in lieu of taxes. It was agreed with George IV, many many years ago. It works.
For those that want a trimmed down royalty, only the Queen & Prince Philip get paid.
For those who think about charity, Prince William donates his wages as an air ambulance pilot, to charity. Many charities wouldn't exist without royal patronage. The Invictus games are the latest,.
Liz? Is that you?