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]
(..) her new emperor. Your loyal subjects bid you welcome, Highness. Thank you, Falco. And for the loyal subjects, - I trust they weren't too expensive. - Caesar. - Gracchus. - All Rome rejoices in your return, Caesar. There are many matters (..)2000 Gladiator