republic.org.uk/what-we-want/royal-finances
I'm just going to leave this here, I know republic are a republican organisation but if you read the report its a much more open, and fairer view of what the Royals cost us. Both organisations have vested interests, I'd back Republic's to be more honest though.
In short, the way the public purse is currently costed the famous "53p " figure per year, is false, it doesn't take into account police protection, maintenence of buildings and whole host of other stuff. They also take into account when doing their figures the money raised from royal lands which belongs to the state and should be calculated and such.
The "Royals bring in tourists" myth is rubbish, even without the Queen there the changing of the guard still happens, it could go on without a Royal family. They may be an "attraction" but they are not the thing that people spend thousands of pounds on to get here. Paris, Berlin, Rome all seem to do well without Royalty, and the Pope waves at the crowds every Wednesday, the Queen does nothing of the sort. The tourists would come anyway and the palaces and their contents could be on show and raise more!
www.theatlantic.com/international/archive/2013/07/is-the-british-royal-family-worth-the-money/278052/
According to the above link they bring in what they claim to cost, but only in a year when there is a Royal event in London.
Earlier on this year there was a thread started about charging for the museums to keep the "rif raf" out, I'd prefer to get rid of the royals first.