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]
(..) Yes, Mrs. Simpson, we can remove your son's tattoo. It's a simple routine involving lasers. - Cool! - However, it is rather expensive, and we must insist on a cash payment up front. - Cash? - Mm-hmm. Thank God for (..)1989 TvShow: The Simpsons Title: Simpsons Roasting on an Open Fire Season: 1 Episode 1