How much of Trump's campaign money has gone to Trump businesses?

Donald Trump largely self-funded his primary campaign. Now, filings submitted to the Federal Election Commission (FEC) show that nearly 20% of the Trump’s campaign spending in May went back to Trump-owned entities. 

It is not illegal to reimburse Trump owned companies

There is nothing illegal about Trump owned companies being compensated for campaign-related services they provide. A review of the filing with the FEC reveals that the expenses were generally in line with the costs of running a presidential campaign.

It is highly unusual for a presidential candidate to have as many personally owned resources as Trump does

What makes the story newsworthy is that it is highly unusual for a presidential candidate to have as many personally owned resources as Trump does. For example, the Trump campaign headquarters are located in the Trump Tower and the campaign paid a little over $700,000 to the Trump Tower for office space, which is the fair market value for leasing space in Trump Towers. Trump is the only major candidate to own his campaign plane and the $349,000 paid to the Trump-owned Tag Air is not out of line with what other campaigns would pay for a leased plane. Where ever possible Trump uses Trump owned properties for campaign events.

Mr. Trump did not appear to be violating any campaign finance laws.
—Ciara Torres-Spelliscy
Election law expert at NYU’s Brennan Center for Justice

In fact, failing to reimburse Trump companies would violate campaign finance law

If Trump’s campaign did not reimburse Trump owned businesses that provide campaign services at a fair market rate, they would be in violation of the ban on corporate campaign contributions.

Still, other wealthy presidential candidates such as New York Mayor Michael Bloomberg and Steve Forbes made it a point that their campaigns avoided using their own branded resources to avoid the kind of questions that are being raised about Trump.

In 2012, Mitt Romney raised an eye-popping $76.8 million in May alone

 The bigger story in the filings with FEC was just how little money Donald Trump has raised. In May, Trump raised only $3.1 million compared to the $28 million Clinton raised. In 2012, Mitt Romney raised an eye-popping $76.8 million in the month of May on his way to raising over a billion dollars.

Trump has less money at this point in the election than any other recent major-party presidential candidate.
The New York Times

Trump says that he’s not concerned about the campaign’s lack of money and says that the campaign could have unlimited cash on hand by Trump simply putting up his more of his own money.

Clinton staffers: 732 Trump: 70

Our campaign is leaner and more efficient like our government should be.
—Donald Trump

The conventional wisdom is that a campaign needs a huge infrastructure to win. Hillary Clinton’s campaign has 732 employees while Trump’s has only 70. Clinton’s campaign has pollsters and voting analysts, while Trump primarily relies on public polling services. Donald Trump is convinced that his unorthodox campaign style will appeal to voters tired of big politics and big money. Time will tell.