The world economy may be bracing for another grim year, but political donors in the United States are breaking out their checkbooks to finance what is expected to be the most expensive presidential election in American history.

The Center for Responsive Politics estimates $6 billion will be spent in the U.S. elections by campaigns, political parties and corporations hoping to propel their candidates into the White House and what writer Mark Twain once called the "best Congress money can buy."

The projected price tag of the 2012 U.S. election dwarfs that of other nations, but corruption monitors from Transparency International (TI) say it's not just how much will be spent but where the money is coming from that threatens the integrity of politics around the world.

While the trajectory for spending in U.S. elections is soaring, total party spending in the 2010 general election in the United Kingdom was actually 26% less than in 2005.

But despite the fact party spending dropped to $49 million, the absence limits on the amount individuals or corporations can donate has contributed to the ongoing erosion of public confidence in the political process in the UK, according to one watchdog organization.

"When donors are making contributions exceeding £20,000 ($31,000) -- and some are making donations well over £250,000 ($390,000) -- it's perfectly understandable you don't give away that kind of money without expecting something in return," Chandu Krishnan, executive director of TI UK.

In November 2011, a UK advisory body recommended increased public funding as one way to avoid future scandals and limit the influence of big donors in elections, but the three main political parties rejected the proposal.

Krishnan, citing Scandinavia as a model, believes increased public funding would cut down party dependence on large donations and give the election system more credibility.

In Norway, government funding accounted for 74% of political parties' income in 2010, according to Statistics Norway. And unlike in the U.S., where candidates and their supporters can buy as much television time as they can afford, political ads are banned from television and radio.

Corruption monitors say the lack of public funding in India, the world's largest democracy, has contributed to a staggering influx of under the table corporate contributions to candidates that has undercut the integrity of recent elections.