Not only did the Trump campaign have less cash on hand at the beginning of June than the suspended campaigns of Ted Cruz and Ben Carson, but it appears that a lot of its spending went into the bank accounts of Trump-related entities, aka The Trump Organization.

The May FEC report showed just 69 people on payroll, to Clinton’s 685. And the Trump campaign’s spending offered no signs that it is building a national campaign infrastructure. The biggest expenditures included $350,000 for the use of Trump’s private jet; $493,000 to rent Trump facilities such as Mar-A-Lago, the Trump winery and two of his golf clubs; and $208,000 on hats.

By comparison, the campaign spent only $48,000 on data management and $115,000 on online advertising.

In 2012, the Obama campaign cleaned Romney's clock with a first-rate system of identifying and then contacting potential voters.  It also owned the world of online advertising. 

As a retired CPA, I'd like to add that the rules that such payments by a campaign to a related party tend to focus on whether such payments were at below fair market value and thus did not cover the actual expenses of providing the service, becoming, in effect, a disguised campaign contribution.  That payments may be overly generous has been far less of a concern.  The reason for this is because campaign contributions are not tax-deductible, while a loss on providing a contracted service would be.  A generous gain on a contracted service, on the other hand, becomes part of the related entity's taxable income.  The rules, therefore, are more concerned that the campaign not screw the taxman than whether it enriches parties related to the candidate at the expense of political contributors.