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]
(..) I don't have any papers. And I'am a foreigner. This climate is exactly what Moriarty wants. The Omelette fino is divine. But they spared every expensive on the tea Now ... You two compare movements, Or consider what we know. last night's bombing was clearly meant to look like Germany's retaliation. (..)2011 Sherlock Holmes: A Game of Shadows