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]
(..) Do you even understand what we are trying to do? Suntory is very exclusive. The sound of the words is important. It's an expensive drink. This is No. . Now do it again, and you have to feel that this is exclusive. O.K.? This is not an everyday whiskey you know. Uh, could you do it slower... (..)2003 Lost in Translation