I've never actually calculated it per meal, seems complicated!
I spend around 100$/week on grocery (just food, no toilet paper, garbage bags, ...) for 2 adults. This yields about 6.5 dinners, 3.5 lunches, 4 breakfast for me (DH doesn't eat much for breakfast) + snacks, sodas, ...! It probably averages around4$/portion on dinner & lunches. We eat tons of fruit & vegetables, meat in small portions, and I do buy pricey foods often (like fancy cheese, duck, smoked salmon ...)
Today's dinner was quite cheap& nice: asian-style sauteed rice, red pepper, & steak with cut-up cucumbers & tomatoes.
3/4c rice: 0.50$??
4 celery stalks: 0.30$
2 onions: 0.20$
2 red peppers: 1.50$
400g steak: 3.50$
1 cucumber: 0.77$
1 tomato: 0.75$
Yield: almost 4 portions (tomato&cucumber are gone, will have to cut more for tomorrow lunches.
dinner price: 2.25$/portion, very good actually!
Meals like this make up for that veal osso bucco with risotto that cost me about 35$ for 4!
I think everyone budget varies depending on what they eat, and their portion size. 100g of meat per portion seems too small for many.

