Re:
All the major Royal Residences belong to the Queen. Tax-Payers Money is used to keep them running, but as far as I know, the Government have never owned the Royal Residences.
Windsor Castle became an issue for the Government after the fire. John Major said that the Government would fund the repairs (but in actual fact, that would be tax-payers money) and there was media outcry. The basic opinion was ' Its her home, she should pay'. In the end, the Queen payed the bill for the repairs and this has made the Royal Family a bit more careful about fire prevention etc.
The big-wigs in finance break down every aspect of Royal Life to decide who should get what. For example;
Princess Alexandra - Widow - Coppins and Thatched House Lodge, Apartment in St James's Palace
The houses are not rented of course. They will probably be owned, either by the Princess herself or by the Queen (Thatched House Lodge and her apartment in the Palace are definately Crown Property). So, the only tab is the upkeep of the properties - gardeners and groundsmen, game-keepers etc. Then you have the 3 footman that are assigned to the Princess. 30,000 a year. (Each one earns about 10,000 a year). Then you have the security which I believe is 4 police men assigned to the Princess. I'm not sure of Police Salary but that could equal 50,000 easily. Then you have everyday bills - water, electricity etc. Her Ladies and Waiting (4 of them) don't get paid. Her Staff and Property would be considered as Business I imagine because she has to have somewhere to live and staff to help her.
She has an office and an apartment in Buckingham Palace complete with a Lady in Waiting, a Press Secretary and a Private Secretary. All have salaries to be paid, as well as office costs for stationary, mailing costs etc etc
Food etc would also be classed as living costs so that comes in to the bill too. Then you have travel. The police escort, the bentley, the footman in the front and the Chauffeur. Again, adds to the Bill.
All this would be paid for by the Civil List - but say the Princess fancies a trip to Biarritz, then she pays for that out of her personal purse. That is a private matter and she wouldn't be expected to give a breakdown of costs (although I imagine it would be made avaliable).
When you add all of this up, you get a pretty high total. She is considered the lower end of the Royal Scale and so for Prince Charles - the costs would be 4 times as much - he has to support Prince William and Prince Harry. As a member of the Royal Family, I think that the Duchess of Cornwall would get a set amount from the Civil List that was set aside from her husband. In the past, Prince Charles took from his alloted fund to support Camilla, but now, she will recieve it personally, the amount given to Prince Charles will account for her or there'll be no extra.
St James's Palace, Kensington Palace etc etc are all owned by the Queen and over the years, they'll have become the property of the Sovereign to do as she likes with within reason. She won't charge rent for her family living there, but they'll have to pay taxes and land costs etc. So, when there was that hoo-hah about Prince and Princess Michael living on a small rent, they probably were only paying the bills we all have to pay and not a rent for the apartment. Their home in Gloucestershire that they are trying to sell (Nether Lypiatt) will be their private home and so the Queen won't own it or have anything to do with it's selling or the new house that they buy.
To sum up my huge waffle, it's a private and public pay-check. Their private finances are exactly that and they can do as they wish, but their public one is dealt with by the tax-payer but that doesn't mean that everything they do with the money can be criticised. The public pay-check is there to ensure that they can carry out official duties and that they can be Royals.
As Ysbel, Prince Charles's expenses to the USA will be picked up by the tax-payer because thats what their pay-check does. If he wants to buy a baseball cap for Camilla, that will come from his private pay-check.