Being the most populous city in India is of no help. Official estimates put the figure at 12.5 million but that figure does not include the millions shanty dwellers and the homeless. Hotel Rooms are very expensive. But mumbai hotels are some of the finest in South Asia. But not everything is expensive.
Food is very cheap.
So is clothes. In fact there is a whole street selling nothing but clothes. No one remembers what the original name of the street is.