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]
(..) What's the problem? You have the money. No, had. I spent almost the whole wad. I mean, I got, like, grand left. I told you, all this crap was expensive. So these thieves, did they say where they would be stealing it from? A chemical supply place, south of town. (..)2008 TvShow: Breaking Bad Title: A No-Rough-Stuff-Type Deal Season: 1 Episode 7
(..) - Damn straight. Okay, hydrogen. Electrolytically produced, yes? Yeah, like you asked. I mean, this... This crap wasn't easy to get. And it's expensive. Methylamine. Where's the methylamine? I don't see the methylamine. Yeah, well, that's where I ran into some trouble. (..)2008 TvShow: Breaking Bad Title: A No-Rough-Stuff-Type Deal Season: 1 Episode 7