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]
(..) All right. We can run right through it. These suits are fire-resistant. These suits are not fire-resistant. They're not? Then why are they so expensive? Bye, Peralta. No! Judy! Both Judys! Judys! Oh, I can't believe this! I really thought I could (..)2017 TvShow: Brooklyn Nine-Nine Title: #DUPE# Season: 4 Episode 11
(..) just got a whole lot... - Let's go! - All right. Whoo. Okay. How do I look? Like I'm about to buy a bunch of expensive art? Hell, yeah. And not just paintings either. You look statue rich. I didn't know we'd have to valet. Perhaps I shouldn't have brought Gertie. (..)2017 TvShow: Brooklyn Nine-Nine Title: #DUPE# Season: 4 Episode 11