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]
(..) It's to be without her. What do the doctors say? You know, with the recent progress, they're gonna keep me alive until . With massages and medication. It's expensive... but I'm a rich quadriplegic. I would shoot myself. Well, you can't even do that when you're tetraplegic. Oh shit. That's right. (..)2011 The Intouchables