Food costs are similar to any big city.
Not true ! If you like chickens feet, ducks spleens, vegetabls that have been sprayed with chemicals left over from 'Nam and rice, it is one of the cheapest places on earth to eat.
Western dairy is 2-300% dearer, unpoisoned fruit and veg same, good meat is only 20% more ( but faark all variety ), fish is pretty cheap if you buy local but be careful as your mercury levels will be full scale deflection within a few years.
Depending on which study you believe Hong kong is somewhere between the most and 3rd most expensive place to live in the world ( that was recentlly )
At 45K you will be close to the lowest paid exat in HKG.
Good luck