Hong Kong food is rice-based and rice is cheap!

Here's some famous advice from Hong Kong's richest man:

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A daily breakfast of vermicelli, an egg and a cup of milk.

For lunch just have a simple set lunch, a snack and a fruit.

For dinner go to your kitchen and cook your own meals that consist of two vegetables dishes and a glass of milk before bedtime.

For one month the food cost is probably $500-$600. When you are young, the body will not have too many problems for a few years with this way of living.

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Note he's talking HKD, and HKD 550 translates into about USD 70.

Unlike rent, everything else in HK can be pretty affordable and it's pretty easy to have decent food for < 5 dollars / meal in HK if you go to non-western places.

There's "This-This Rice" places (Rice + 2 other ingredients like meat / vegetables) that usually have big portions and feel somewhat healthy.