Her decision to leave the company proved to be an 'expensive' mistake. [=a mistake that caused her to lose a lot of money]
They live in an 'expensive' neighborhood. [=a neighborhood in which houses, apartments, etc., cost a lot to buy or rent]
an 'expensive' shop [=a shop that sells expensive things]
(..) Does this sound fancy to you? Nah, just sounds like gold clinking up against crystal. What? Those are two of the most expensive things! Relax, dude, it's not a competition. I just got something from the "lost and found" bin at work. I don't want people spending money they might not have tomorrow. (..)2017 TvShow: Superstore Title: Cheyenne's Wedding Season: 2 Episode 20