At Mar-a-Lago on a Wednesday evening last month, Donald J. Trump mingled with partygoers, greeting his supporters and making small talk. The country star Lee Greenwood sang “God Bless the U.S.A.,” and the former president’s oldest son, Donald Jr., gave a speech.

The elder Mr. Trump was presiding over a cocktail reception for about 150 guests to celebrate the public debut of Trump Media & Technology Group, the parent company of his social media app, Truth Social. Trump Media’s share price had soared in its first day of trading, adding billions of dollars to Mr. Trump’s wealth.

But the party was far from lavish. Guests munched on cookies emblazoned with the letters DJT, the company’s stock symbol. They were invited via the free Paperless Post app and told they couldn’t bring a plus one, according to a copy of the invitation.

Mr. Trump was not shy about the frugality. A benefit of Truth Social, he told guests, is that it is “not very expensive to run.”

From the moment Trump Media was founded in 2021, Mr. Trump has treated it as a low-cost, low-effort venture. While he once served as chief executive and owns nearly 65 percent of the company, he has been only marginally involved in its day-to-day operations, mostly posting on Truth Social and delegating the business to others. At times, he considered working on competing ventures, according to court filings, corporate records, and five former employees and others familiar with the company.