Define "healthy foods" vs. "unhealthy foods" because I suspect you're fooling yourself. What's your per-person budget?
Root vegetables, greens, wheat flour, dry legumes, brown rice, chicken, olive oil, fruit.
vs. "unhealthy foods"
Potato chips and other packaged snacks, packaged cookies, soda, premade burger patties, fried chicken, ice cream, most breakfast cereals, jelly.
because I suspect you're fooling yourself.
Not really.
What's your per-person budget?
Fairly low, because I buy in bulk. Beans, rice, flour and oil keep for a long time. Root vegetables keep for a decent amount of time. You can buy meat cuts on sale and freeze them and buy a week's worth of greens on sale too.
In theory, I could buy 10 boxes of donuts on sale and eat them for a week, or I could buy prepackaged organic "healthy meals" from Whole Foods for $20 a pop. You can make either kind of eating as expensive or as cheap as you like.
In the average grocery store you can find healthy food on sale and unhealthy food on sale. But you can live for a week on chicken stew with beans and squash and wheat bread much better than you can live on Ho-Hos, Frito Lays, hotdogs and RC Cola, even if you bought them at the same price.