What price for the best Ford Sierra Cossie in the world? In 1987 the black RS500 would have set its first owner back £20,000. At the weekend auctioneers reckoned the unmarked 5,192-mile example would fetch a mind-boggling £180,000. But today we know the truth and it wasn’t mind-boggling at all. It was utterly gob-smacking. It sold for almost £600,000.