Candidates and supporters will spend at least $3.7 billion in the 2010 midterm elections, according to a new report.

The estimate reflects more than a 30% increase from the 2006 midterm elections, and would represent the most expensive non-presidential election cycle ever.

"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 the Center for Responsive Politics, which released the report.

What's more, the estimate does not include independent expenditures by corporations and unions, which will be legal in 2010 thanks to a recent Supreme Court decision.

CPR characterized the estimate as "conservative," and Krumholz called the estimate "solid baseline to compare new spending levels against."