“I would guess that based on recent history, we would see a more expensive election cycle than in 2010,” said Sarah Bryner, research director for the Center for Responsive Politics, “and that I think is driven largely by what we call outside spending, super PAC spending and political activity by political nonprofits.”

In 2010 and 2012, campaign spending in congressional elections hovered near an eye-popping $3.6 billion , including $1 billion in independent expenditures. Observers agree that the current upward trajectory of money spent on campaigns is fueled by these loosely independent outside groups, which were given rein to spend unlimited sums by the blockbuster Supreme Court Citizens United v. FEC decision in 2010.

Much more is expected to flow in as candidates vie in competitive primaries and the general election season gets into full swing.

Early indicators suggest that 2014 could see the most expensive midterm elections in U.S. history. Candidates have officially collected $446 million through their campaign committees, according to data collected by the Center for Responsive Politics . Most worrisome for many concerned about the avalanche of money in the political system is the cash originating from a few wealthy donors and corporations, then funneled through outside groups like trade associations, nonprofits affiliated with political causes, and commitees, or "super PACs," closely allied with candidates. These so-called independent expenditures have already topped $25.5 million for 2014 and the 2013 special elections . That figure outpaces the $21.2 million spent at this point in the 2012 cycle and dwarfs the $8.5 million spent by this time in 2010.

It’s still 10 months from Election Day, but the amount of money raised to fund this year’s congressional races already numbers in the hundreds of millions.

Moreover, in past election cycles, conservative and Republican-affiliated groups tended to dominate independent expenditures, but signs are that Democrats too will fully embrace outside money in 2014. Groups like Planned Parenthood, EMILY’S List, the liberal American Bridge, and the House and Senate Majority PACs will all be spending on behalf of Democratic candidates across the country, particularly in an effort to defend the party’s fragile Senate majority.

“We’re likely to see a lot of the trends (that were there) in 2012 but bigger, and that all relates to the Citizens United decision and the court’s decision that corporations and groups could spend unlimited amounts of money,” said Lawrence Norden, deputy director of the Democracy Program at the Brennan Center, a campaign-finance-reform advocacy group. “In the very hotly contested primary races or in the general election, we saw huge amounts of money coming from the outside, super PAC money, 501(c)(4) money, and in the primaries you had what looked like candidates being sponsored as if they were racehorses by certain people.”

Paul S. Ryan, senior counsel for the Campaign Legal Center, said he’s not as concerned about the volume of money as he is that so much of it is coming from a select few megadonors and the original source is often cloaked in secrecy, as is allowed by the current labyrinth of mechanisms available to donors who want to remain anonymous but contribute huge sums.

“If the money was coming in small chunks from voters, the Campaign Legal Center wouldn’t be as troubled,” he said. “We have campaigns taking huge contributions, not disclosing the true original source of those funds, and most importantly we think these huge contributions pose the threat of corruption.”

Candidates in competitive Senate races have already amassed impressive war chests, such as in Kentucky, where Senate Minority Leader Mitch McConnell is trying to stave off challenges both from within his own Republican Party and a Democratic opponent; and North Carolina, where vulnerable Democratic Sen. Kay Hagan is trying to defend her seat against a yet-to-be-determined Republican opponent.

The most expensive Senate race in history occurred in 2012, when Democrat Elizabeth Warren defeated Republican Scott Brown for a Massachusetts seat at a price tag of $82 million. This year might shatter that record, too.

“With the Senate in play, we may see races going over $100 million — in Kentucky you have a very powerful politician, his approval ratings are quite low, but one of his assets is that he’s in the position to raise huge amounts of money directly,” said Nick Nyhart, the president of Public Campaign, a group advocating for a federal public financing system. “Every cycle it will get worse.”