“The 2012 election will not only be the most expensive election in U.S. history, the cost will tower over the next most expensive election by more than $700 million. Earlier this year, the Center for Responsive Politics estimated that the 2012 election would cost $5.8 billion — an estimate that already made it the most expensive in history — but with less than a week to go before the election, CRP is revising the estimate upwards. According to CRP’s new analysis of Federal Election Commission data, this election will likely cost $6 billion.”
http://www.opensecrets.org/news/2012/10/2012-election-spending-will-reach-6.html