[James]

It's not surprising when you see how much it costs to get elected in the US.

I found this.

In 2008, candidates for office, political parties, and independent groups spent a total of $5.3 billion on federal elections.[2] The amount spent on the presidential race alone was $2.4 billion,[3] and over $1 billion of that was spent by the campaigns of the two major candidates: Barack Obama spent $730 million in his election campaign, and John McCain spent $333 million.[4] The total amount spent by Obama and McCain was a record at the time.[5]

In the 2010 midterm election cycle, candidates for office, political parties, and independent groups spent a total of $3.6 billion on federal elections. The average winner of a seat in the House of Representatives spent $1.4 million on his or her campaign. The average winner of a Senate seat spent $9.8 million.[6]

http://en.wikipedia.org/wiki/Campaig..._United_States

The size of the country is always going to make it expensive, and also the fact they spend a lot on political TV advertising.