Even a billionaire could not afford to spend $500 million on a presidential campaign where you may or may not get elected.
Also, imagine you were applying for a job and it costs you money for a resume, a suit, etc. The president is paid $400,000 a year, why would you spend $500 million to get a job that pays you $400k a year for four years? You are not even going to make 1% of the money you spend on the campaign.
Also, no one can possibly have all the skills and know how for this. There are thousands of jobs to appoint if you are elected. Once elected you would need to make about 10-20 appointments per day up until inauguration and I suspect the briefings that go on probably take up half your day every day of that time (by half a day I don't mean 4 hours).
My point is the candidate is simply the tip of the spear. This is why as soon as someone wants to be a third party candidate it is a joke. If you don't have the machine behind you then you really have no chance.
Which brings me to the real point, the US election is two very big machines running everything. It is like going to McDonalds and you have a choice between the Big Mac and the Quarter pounder with cheese.
Now you may rightly feel that this election is far more acrimonious than that would be, and that is true. It isn't because of the machine, it is because within the political system there are people who have a conscience and are taking a stand for Jesus. If that were not true you wouldn't see any of this. Jesus said that a house divided cannot stand and Satan cannot cast out Satan. We saw that, RINOs could not cast out Democrats because they are all part of the same block of cheese. Any success we are seeing at exposing the corruption in the US government is because you have people standing against all odds for righteousness. Because of that Satan is no longer able to maintain the illusion of democracy. But pulling away the curtain from the little man behind the curtain is not the same thing as defeating the wicked witch of the West.