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]
(..) No peeking. Four. Are you guys done with the pizza? I don't want it going to waste. - Let's go. - It's expensive feeding you girls. Seven, eight, nine, ten. Where should I hide? Ready or not, here I come! Okay, clap. - Whoa! (..)2013 The Conjuring