When all is said and done, the 2010 election is likely to cost more than $3.7 billion, more than any other mid-term election, according to the Center for Responsive Politics.

CRP made the prediction based on historic spending increases in previous mid-term elections. The center said election spending has increased by 31 percent to 35 percent from cycle to cycle. About $2.9 billion was spent in the 2006 election cycle.

"With so much on the line, the outpouring of big money into federal campaigns looks likely to continue at a brisk pace," said Sheila Krumholz, executive director of CRP. "Additionally, the recent Supreme Court ruling in Citizens United v. Federal Election Commission could precipitate millions more in spending by special interest groups looking to advance their own agendas."

Included in the estimate is spending by Senate and House candidates and political parties, as well as 527 committees and independent expenditures on advertising and get-out-the-vote efforts. It doesn't include expectations of boosted spending by corporations as a result of the Citizens United case.