The total cost of the 2012 elections will exceed $6 billion, according to new projections released today by the Center for Responsive Politics.

CRP upwardly revised its estimate based on accelerated spending by outside groups, which doled out $70 million for and against the two main presidential candidates during the week beginning Oct. 21. That compares with $33 million a week in early October and $19 million a week in early September.

Driving the outside spending are unrestricted super PACs, which have put $539.5 million into the race so far. CRP projects that super PAC spending will eventually hit $587.4 million. Corporations, unions, individuals and other groups collectively spent $351.3 million through Oct. 31. Political parties have spent $215.1 million.

“This will still be the most expensive election in U.S. history,” CRP Executive Director Sheila Krumholz said at a briefing today with reporters. Earlier this year, CRP predicted that the price tag of the 2012 elections would total $5.8 billion, already a record. The 2008 contest cost $5.3 billion.

Overall spending on the presidential race — including the money invested by candidates, parties and outside groups, — will reach $2.6 billion in this campaign, a slight drop compared with the $2.8 billion spent on the presidential contest in 2008, according to the CRP. The dip is “unusual,” acknowledged CRP senior fellow Bob Biersack, but can be explained by the lengthy and competitive nature of the 2008 presidential primary season.

House and Senate candidates combined will spend some $1.82 billion this cycle, CRP projects, a slight increase from 2010. Incumbent lawmakers enjoy a huge advantage over challengers, with the average incumbent Senator raising $11 million over a six-year term, a nearly 10-to-1 advantage over a Senate challenger’s average haul of $1.2 million.

The average incumbent House Member raised $1.5 million, compared with a comparatively meager $245,000 collected by the average House challenger. On average, open seat House candidates have collected more than $453,000. Democratic Senate candidates outraised their GOP counterparts by an average of $3.8 million to $2.6 million. But House Republican candidates did better than Democrats running for that chamber. House GOP hopefuls collected an average of $712,000, compared with $594,000 raised by their Democratic opponents.

Outside spending has also escalated in Congressional races. In the week beginning Oct. 20 alone, outside spending totaled $41 million in the 59 House contests that Real Clear Politics rates as either tossups or leaning to one party.

Big spenders have somewhat shifted their allegiances since the 2008 presidential race, according to the CRP’s analysis. Donors from the finance, insurance and real estate sectors still dominated, but Wall Street donors, in particular, pivoted from President Barack Obama to GOP nominee Mitt Romney. Wall Street has put $28 million into the election to date, but $19.6 million of it has gone to Romney, three times what went to Obama.

Lawyers and law firms, by contrast, sent Obama $25.7 million of the $40.2 million they have invested in the presidential race through Oct. 17. That’s a smaller share than Obama’s 2008 haul from the lawyers and law firms of $46.5 million, but still twice what Romney has collected.

Additional hundreds of millions have been spent by non-disclosing outside groups, including tax-exempt social welfare organizations and trade associations that target candidates with high-dollar “issue” ads not subject to disclosure rules. At least $100 million to $200 million has been spent by such groups, according to the CRP.

“This is going to be a puzzle that we will put together over the weeks and months to come,” Krumholz said.