ford sensers are about £70 iirc, it's possible the eshaust will need to be removed, but i highly doubt it. if he's unsure what senser needs to be replaced, i'd advise your boss took the car to a ford garage. it's highly unlikely the 2nd senser will need to be replaced, if driven for a while though it will damage the cat and i think the cat and manifold is one piece on these=expensive.