President-elect Donald Trump on Wednesday said he would personally “negotiate the prices” with Boeing Co. of the planes to be used as Air Force One, promising to block a future order if necessary and to continue using the existing aircraft for the presidential plane.

Mr. Trump, in a Wednesday morning interview on NBC, said he had spoken to Boeing Chief Executive Dennis Muilenburg on Tuesday following criticism Mr. Trump leveled at the company about what he perceived were elevated prices for the planes. Mr. Trump accused the...