Mr. Biden has continued to pursue commercial activities while he is in the final stage of making a 2020 decision; he is scheduled to give a talk in Grand Prairie, Tex., a suburb of Dallas, on Thursday, as part of an extended tour promoting his 2017 book, “Promise Me, Dad.”

The speaking contract for Mr. Biden’s October appearance in Michigan suggests that the popular Democrat would have known he was addressing a Republican-leaning crowd. The speaking series was underwritten in part by organizations connected to Mr. Upton’s family: Among the biggest sponsors listed on the Economic Club’s website are the Whirlpool Corporation, which was co-founded by Mr. Upton’s grandfather, and the Frederick S. Upton Foundation, a family charity named for the same man.

The contract for Mr. Biden’s visit shows he was paid $200,000 for his appearance, including a $150,000 speaking fee and a $50,000 travel allowance. It also specifies that the audience would be “primarily older, conservative Republicans and local community members.” The document was disclosed in response to a Freedom of Information request made by America Rising, a Republican group that conducts research on Democratic candidates.

It is unclear whether the fees Mr. Biden received in this case are standard for all his speeches. Mr. Biden’s aides have declined to confirm what his rates are for paid appearances, including the appearance in Michigan, or how much he has earned through paid speaking since leaving office. In at least one instance, his speaking bureau, Creative Artists Agency, offered a reduced rate of $100,000, plus travel expenses, to the University of Utah.

If Mr. Biden were to have charged a similar range of fees for all his comparable speeches since leaving office, he would most likely have collected between $4 million and $5 million through speeches over the last two years.

Representatives of Lake Michigan College, which recently took over management of the Economic Club speaker series, and the Fredrick S. Upton Foundation confirmed that the Upton organization was a major sponsor of the series. Both organizations said Mr. Upton had no role in proposing or choosing the speakers. Lisa Cripps-Downey, president of the Berrien Community Foundation, a nonprofit that administers the Frederick S. Upton Foundation, confirmed that the organization had given substantial funding to the Economic Club, with an annual grant of $80,000 over the last three years — a total close to a quarter-million dollars.

“When we see the speakers, we’re just as surprised as everybody else,” Ms. Cripps-Downey said.

Mr. Russo said Mr. Biden’s team had been aware that the Frederick S. Upton Foundation helped fund the Economic Club. He said Biden aides had vetted the funding sources for the speaking series and concluded they met his standards.