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]
(..) and release it into the wild. Spoons. That's it, I'm out of ideas. We're closed. Hot air balloon? Too expensive. Giant slingshot? Too conspicuous. Enormous wooden horse? Too Greek! ( speaking baby talk ) (..)2001 Monsters, Inc.