Since May, the president has gone to 69 fundraisers, each with ticket prices topping tens of thousands of dollars. His opponent, Republican Mitt Romney, has held 105 of the donor events, in a frenzied race for money that has already pushed this year's presidential campaign coffers past $1.3 billion.

While the sum may seem staggering, the 2012 edition of the presidential race shouldn't cost significantly more than in 2008 since the president didn't have to finance a primary campaign to win the Democratic nomination.

As of August 31, Barack Obama had raised $432 million, less than the $746 million collected four years ago, according to figures filed with the Federal Election Commission.

In comparison, Romney had raised $274 million, just below John McCain's haul of $288 million.

But the numbers don't stop there.

On top of the campaign fundraising efforts is the money raised by the national Democratic and Republican parties -- $233 million and $283 million, respectively -- and independent partisan groups, or super PACs, which have raised $36 million for Obama and $97 million for Romney.

And while Obama has not yet reached the staggering heights of his 2008 fundraising success, he remains the uncontested king of small-scale donations: 37 percent of the checks sent to his campaign are made out for less than $200.

His multimillionaire rival's coffers count just 16 percent of their take from small-scale donations, according to figures compiled by opensecrets.org.

But the Republicans make up for the lag with an avalanche of money from rich individuals, free to contribute unlimited sums to the "friendly" political action committees following recent changes to campaign finance regulations.

Only half of the pro-Romney ads broadcast in September were paid for by his campaign, according to Kantar Media/CMAG data with analysis by the Wesleyan Media Project, a university research center that studies political advertising expenditures.

The rest were paid for by organizations free to raise unlimited money from rich individuals, corporations and unions, thanks to a 2010 Supreme Court decision on campaign finance reform.

The Citizens United ruling said that corporations, unions and individuals could make unlimited contributions to partisan political groups, as long as the organizations were "independent" of the candidates.

Two types of outside groups exist: Super PACs, which are required to make public the names of their donors, and groups known by the legal code 501(c)4, non-profits ostensibly operated exclusively for the promotion of "social welfare" such as churches and environmental groups.

The latter do not have to reveal their donors, but can only use half their expenditures for political activism, though that limit is not generally enforced.

So who sends checks to top Republican super PAC American Crossroads, run by right-wing strategist Karl Rove, with a budget of around $300 million?

At the top of the list, with a donation of $10 million, is billionaire Harold Simmons, chief executive of the industrial group Contran Corporation. Not far behind is Bob Perry, head of the construction firm Perry Homes, with a $6 million check.

And the list goes on, with dozens of other conservative business titans capable of doubling overnight the resources of their camp.

The Democrats, too, have their super PACs. Unions, which overwhelmingly support Barack Obama, have launched Priorities USA Action -- though it has raised less money than its Republican counterparts.

But the strongest impact will be seen in legislative elections, where a relatively small boost of just a few million dollars can completely a race, said Michael Malbin, executive director of the Campaign Finance Institute.

American Crossroads and its 501(c)4 partner "Crossroads GPS," whose donors remain secret, have dedicated half of their spending on local races, in hopes of regaining a majority in Congress and blocking the Obama agenda if he's re-elected.

WHERE THE MONEY COMES FROM

Spending on the 2012 US presidential race is likely to exceed the record $1.8 billion that the candidates spent in 2008, according to projections based on figures filed with US election authorities.

The 2008 race was marked by fiercely contested fights for the Democratic and Republican presidential nominations, but Democrat Barack Obama ran unopposed this time and Mitt Romney secured the Republican nod relatively early.

Most notable this electoral cycle has been the emergence of so-called super PACs, special political action committees that operate independently from the candidates and can raise unlimited amounts of money.

Amount raised by the campaigns of the presidential candidates

- Barack Obama: $432 million

- Mitt Romney: $274 million

Source: Federal Election Commission, August 31

Amount spent by the presidential candidate campaigns

- Barack Obama: $354 million

- Mitt Romney: $233 million

Source: FEC, August 31

Amount raised by the parties

- Democratic National Committee: $233 million

- Republican National Committee: $283 million

Source: FEC, August 31

Amount raised by "Super PACs"

- Priorities USA Action (Obama): $36 million

- Restore Our Future (Romney): $97 million

Source: Center for Responsive Politics, opensecrets.org, August 31

Amount spent by independent groups at national and local level

- Liberal groups: $374 million

- Conservative groups: $147 million

Source: Center for Responsive Politics, opensecrets.org, October 10

Number of fundraisers between May 29 and October 10

- Barack Obama: 69

- Mitt Romney: 105