50,000 pesos a month from a small grocery store is very unrealistic.
I agree. My aunt opened a small grocery / convenience store a few years ago as an extra source of income, despite not knowing anything about running one. She closed it after 6 months. She lost money on the venture.
The store was open 12 hours from around 7am to 7pm for security reasons. But not too far was a convenience store chain that was open 24 hours.
They were hoping that the students of the college across their street would go to their shop. But most of the students were from low-income families. And sometimes students would shoplift. Often bought items by students were school supplies and instant noodles. The store charged extra for hot water heated by an electric kettle.
Refrigerators and freezers (for things like soda, water, ice cream products, etc.) were provided for free by suppliers. But these use up a lot of electricity. They hired a cashier part time. But they caught him giving in to discounts asked by young and pretty customers.
Then there's the initial cost of building the store: cabinetry, storefront, counters, shelves, flooring, painting, etc., including fees for city permits, DTI license, BIR registration, printed invoices and receipts, etc.
I think if my aunt really thought things over before starting the store, such as just getting a self-bought energy efficient refrigerator / freezer, better floor plan to avoid shoplifting, included cheap meals for students, and just managed the store herself, i.e. not hiring employees, she probably would have had an average of PhP20k profit per month, not PhP30k to PhP50k.
A well-managed sari-sari store could earn the same depending on location (near a gathering place like a park, basketball, town plaza, barangay hall, no nearby competition, the neighbors have kids and are ok with cheap brands / non-brand items, etc.), if it's well-managed (self-run, no credit, no family members getting free stuff, inventory sourced from wholesalers). One can also do "re-packing" (my assistant did this at one time) where you buy bulk items, and re-package them in small plastic bags, such as garlic, candies, chlorine grains, etc., which you can sell at your store or to other sari-sari stores.