If you factor in revenues from the Crown Estate – in name at least the monarch’s property portfolio – which are handed over to the Treasury (c 183m PA, although probably a bit less at the moment), then it’s clearly not all one way traffic.
Crown Estate includes physical property – quite a bit of the West End, and stuff like foreshore rights along the coast.
You could argue that these are not actually owned by the Queen, but effectively by the state, and that she would not have the legal right to take these revenues back at present. However, it’s not hard to see a historical situation where a more thorough separation of royal family and state would have left those assets, or most of them, in the royal family’s hands.
It’s certainly worth bearing in mind when looking at the full equation.
Liz and her clan as ordinary citizens would not perform civic duties – my understanding is that a fair sum of the civil list is spent on staff organising those functions, rather than paying for Bentleys.