Why do they cost so much money? - 2016 U.S. Presidential election

Here's what you need to know about the 2016 U.S. Presidential election. One reason they cost a lot is because they last so long.
Unlike some other countries, there are no rules on how early a candidate can start campaigning - Ted Cruz officially announced he was running in March 2015, nearly 20 months before the election.
Also unlike some other countries, there's no limit on how much you can spend.
A presidential campaign can cost up to $1 billion - and that's not even counting money spent by outside groups.
 It's not cheap to travel across the country for two years or more, buy advertisements on television, and pay a small army of campaign workers.