Akenaton,
The campaigns (candidates) raise money. *That* is about equal (albeit from different sources...Obama gets 55% of his money from donations less than $200 while Romney gets 45% of his money from donations above the $2500 limit). Other groups can raise and spend as long as they do not coordinate with the campaigns. This money is many times larger than the actual campaign money, and Repubs raise 10X what Dems do in this.
And yes, disgustingly, in the USA, the candidate that spends the most money (or has the most spent on him/her by outside groups) wins the election over 75% of the time.
That is why US progressives have been fighting Citizens United so hard. Our elections can, in fact, be bought.
We used to be one person - one vote.
We are now one dollar - one vote.