The Panama Canal is a man-made construct and costs money to operate. How is that comparable?

It's comparable in that it's a nearly-identical construct that functions in an actually-identical way. Constructing the Strait of Hormuz was cheaper than constructing the Panama Canal.† That doesn't change anything about the fact that it exists.

† Cheaper in an abstract sense. In a more literal sense, the tolling authority, Panama, didn't have to pay for the canal; it was built by the United States.