The palace (Istana Nurul Iman) of HM the Sultan of Brunei in the capital Bandar Seri Begawan was completed in January 1984 at a reported cost of £300 million ($422 million). It is the largest residence in the world, with a floorspace of 200,000m2 2152780ft2, 1788 rooms and 257 lavatories. The underground garage accommodates the Sultan’s 153 cars. 

Rate of exchange Jan 1984 – 1.4082 = $422.46