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 know, this is not as creepy as you may think. She is my loving tribute to you. Isn't she beautiful? She's a fuck doll, Stu. She's an expensive fuck doll... large. But... But she's so much more than that. She's a woman, just like you. And I have made love to her, just like I made love to you. (..)2014 TvShow: Californication Title: Grace Season: 7 Episode 12