Baffling

£5 billion? I don't know the actual cost, but it can't have been anything near that high. Taxpayer's money was only paying for security and transport, the rest was covered by the families. I do know that the cost of security for the Pope's visit last year was about £10 million, and security for the 2009 G20 hobnob in London was roughly £7 million. The wedding would surely be a similar order of magnitude.

There may also be a loss to the total economy because of the extra bank holiday, but how much (and whether it is countered by extra tourism, memorabilia etc.) is a matter of debate: http://blogs.wsj.com/numbersguy/how-much-did-royal-wedding-cost-britain-1055/