Even someone like Donald Trump cannot afford to run for president by himself. It would badly hurt his wealth and would not be worth it. Maybe he funded the start by himself, but when things got more serious, ofcourse he found donators for his campaign.
You obviously don't know much about Donald Trump.
https://www.opensecrets.org/pres16/and
https://www.opensecrets.org/pres16/candidate.php?id=N00023864His net worth is well over $4 billion. If he spent $200 million on his campaign, which he doesn't need to do, it would cost him 5% of his net worth. A years worth of interest, basically.