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]
(..) you get earthquakes in California. Wonderful! Couldn't have said it better myself. Everything west of this line is the richest, most expensive real estate in the world. San Diego, Los Angeles, San Francisco. Everything on this side of the line... ...is just hundreds of miles (..)1978 Superman