I live in Suburban Manila but Metro Manila is my usual haunt when it comes to shopping in malls. If you want to know that food costing $20, that's in an upscale commercial area called Capital Commons which is designed for the rich.
It depends but for those of us that always have their food at home we'll be spending a lot less. Since I formed the habit of cooking and eating at home our spending on food is low. We shop for raw foodstuffs once in a week and raw foodstuffs are cheaper . I'd say with around $50 we get plenty foodstuffs that can last for a week.