What is the ruling on the fare that a driver receives from transporting a woman who does not have a mahram accompanying her, and is this fare considered unlawful if the transportation itself is unlawful?

A number of scholars have issued a fatwa prohibiting a woman from riding alone in a car with a non-mahram driver, because it constitutes unlawful seclusion (khalwa). As for the fare for the ride, it is permissible, because it is a wage for a permissible matter.