Mr. Trump has pointed to Mrs. Clinton’s noticeably scant schedule of campaign events this summer to suggest she has been hiding from the public. But Mrs. Clinton has been more than accessible to those who reside in some of the country’s most moneyed enclaves and are willing to spend hundreds of thousands of dollars to see her. In the last two weeks of August, Mrs. Clinton raked in roughly $50 million at 22 fund-raising events, averaging around $150,000 an hour, according to a New York Times tally.