A new report from Redfin underscores just how swiftly the luxury real estate landscape has shifted — but buyers in certain Rust Belt markets can find deals.

Five years ago, you could buy a luxury home for less than $1 million in 30 major U.S. cities—that number has shrunk to only seven.

The reason there's even a debate, as it were, over the dollar signs going into David Corenswet's Man of Steel is due in part ...