He owns a lot of real estate and collects a lot of rents like Donald Trump. If the Queen's list of "those who take money from the public purse" were to be completely expunged the Royals would still survive intact. THey wouldn't be able to keep all their medieval castles and would give them to the national trust due to tax problems.
The UK govt receives far more money from the Royals than the royals receive from the govt. In 2004 the crown estates made a profit of £184.8m and govt money given to the monarchy and to fund buildings etc, etc was £36.8m. The Civil List is now set at £7.9m per annum and only funds Her Majesty the Queen and the Duke of Edinburgh - all the other royals have to self-fund or ask their mom to help out.
When one includes the huge amount of tourist money brought into the country by the monarchy, I suspect they actually generate a net profit for the country.
I doubt you could run Air Force One for a year on what the civil list costs the UK taxpayer and the upside is we never end up with grubby democratic politicians like Carter or Clinton as our head of state going abroad and embarrassing us. . . . . ;-)