This is in the EU, regulation basically prevents excesses like that in most cases.
Furthermore, price doesn’t have to be a predictor of quality. E.g. LIDL/Aldi (budget chains) commonly win awards for best vegetables.
I used to spend ~150-200 on food per month when I was living by myself and wasn’t strictly managing it for low cost. Now with a family of 3, we spend 300-400€ a month on groceries (incl bread and meat) and are never holding back on anything because of price.
So, 5€ per day doesn’t sound unreasonable even in the Netherlands. Note: we eat vegetarian 5 out of 7 days, without that we’d probably spend 100-150 more.
Edit: I get that this doesn’t work everywhere. When I lived in the US (NYC) and tried to cook my own meals I couldn’t believe 1) how few supermarkets there were and 2) how high prices for basic food were. Eating out was basically cheaper :/