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]
(..) something you can discuss? What? It's very simple, Stella. She belongs to that rarefied atmosphere of Park Avenue! expensive restaurants and literary cocktail parties. People with sense belong wherever they're put. Can you imagine her tramping around the world with a camera bum... (..)1954 Rear Window