(CNN) -- Cory Booker raised an eye-popping $4.6 million over the past three months for his bid in the New Jersey special election for the U.S. Senate.
The Newark mayor's cash haul that was announced Thursday is the latest example of the skyrocketing costs of winning election or re-election to Congress.
Last year, winning Senate candidates spent an average of $10.3 million, according to the latest edition of Vital Statistics on Congress, which was released this week. That's a 62% increase, adjusted for inflation, since 1986. The report indicates that it took, on average, $1.6 million to win a House seat in 2012, a 344% increase since 1986.
That increase is dwarfed by spending of outside independent groups, especially following the Supreme Court's Citizens United decision in 2010. That ruling removed legal barriers preventing corporations and unions from spending unlimited sums on federal elections.
Outside groups spent $457 million on Senate and House races in 2012, according to the report, compared to $9 million in 1986. In 1978, such groups spent only $303,000 to influence Senate and House elections.
"The most striking to me is the explosion in outside spending," said Norm Ornstein, a resident scholar at American Enterprise Institute, which contributed to the report.
"The numbers for (political action committees) become a surrogate for the huge amounts outside what candidates and parties spend themselves. So for House Republicans, the nightmare is the Club for Growth (an independent fiscal conservative group) spending big money to challenge incumbents like Mike Simpson from the right, meaning the party is pulled even further to the right," Ornstein said.
"And for all incumbents, the fear of an alien predator individual or group parachuting in behind the lines in the final two weeks of the campaign with a multimillion dollar ad blitz means they spend even more precious hours doing call time to raise money," he added.
But the report, which uses Federal Election Commission data compiled by the non-partisan Campaign Finance Institute, indicated that incumbents in both the House and Senate, not surprisingly, tended to outspend their challengers.
But the fund-raising disparity was far more pronounced in House races.
On average, House incumbents outspent their rivals $1.7 million to $587,000, a ratio of almost a 3-1. Incumbent senators spent on average $10.7 million compared to $7.2 million for challengers.
Challengers narrowed the spending gap with incumbents in competitive House races but not by much. Incumbents who were re-elected with less than 60% of the vote raised on average $2.3 million in the 2012 cycle, slightly more than double the $929,000 spent on average by their challengers.
Incumbents re-elected in competitive Senate races still outspent their rivals but by a much narrower gap of $12.8 million to $10.1 million.
The report also shows that outspending opponents did not necessarily guarantee victory. House incumbents who lost their re-election bids in 2012 on average spent more than their challengers -- $3.1 million to $2.5 million.