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]
(..) in action, suntan - Afghanistan or Iraq. You said I had a therapist. You've got a psychosomatic limp, of course you've got a therapist. Then there's your brother. Your phone. It's expensive, e-mail enabled, MP player. You're looking for a flatshare. You wouldn't buy this - it's a gift. Scratches. (..)2010 TvShow: Sherlock Title: A Study in Pink Season: 1 Episode 1
(..) He's always like that. Hello. - Ah, Mr Holmes. - Sherlock, please. Well, this is a prime spot. Must be expensive. Mrs Hudson, the landlady - she's given me a special deal. Owes me a favour. A few years back, her husband got himself sentenced to death in Florida. I was able to help out. (..)2010 TvShow: Sherlock Title: A Study in Pink Season: 1 Episode 1