Did any of you read the wikipedia link I posted?
First paragraph of the article:
The British Royal Family is financed mainly by the hereditary revenues of the Crown.[1] The British Parliament uses a percentage of the Crown Estate, a part of the Crown's hereditary revenues belonging to the sovereign that is placed at the disposal of the House of Commons, to meet the costs of the sovereign's official expenditures.[1][2] This includes the costs of the upkeep of the various royal residences, staffing, travel and state visits, public engagements, and official entertainment.
As far as I can make out, the Treasury receives the income from the Crown Estates and a percentage of that is paid to the Queen as the Sovereign Grant. She and Prince Charles also pay the Teasury a voluntary amount each year from their private income equivalent to what they would have paid in income tax had they been liable for income tax. So, apart from the cost of security (a figure for which I haven't been able to find) I can't see where any cost to the taxpayer is involved.
Historically all the land in a country belonged to a monarch, who then parcelled it out to their followers in reward for services to the Crown. That's how many of the huge landholdings of the 'aristocracy' were originally acquired. The Crown Estates are what is left after centuries of dishing out land to the favoured.
The Duchy of Cornwall was given to the monarch's heir in mediaeval times; that's what suppports Prince Charles and his family. Both he and the Queen are perfectly entitled to give whatever they want to members of their family out of their private incomes and properties; it's how any wealthy family behaves.