$1.40/lb for frozen chicken breasts is a sale price, but it's not out of the ordinary for what I used to see in Seattle (less than a year ago) or what I see in rural Utah now. $2-3/lb is more common, and I've seen similar prices when I visit family in Denver, the Oregon coast, and northern Cali. I don't know why Chicago is $4-7/lb for "the grocery store crap"; all I know is that those numbers are way outside of the prices I've experienced. The prices I gave are not "ludicrously unrepresentative"; they're prices I see on a regular basis.

I'm a stay at home dad who's done the shopping for many years. I shop at the closest store, tilt my shopping somewhat but not entirely toward sale items and generics, and don't do anything more extreme than grab coupons from the ads at the customer service desk. I'm not doing anything out of the ordinary, or anything that I'd expect "the poor" to have trouble doing. Everything I say here is a result of my experience feeding my family in a way that I think is pretty normal and sensible. In my experience, home cooking comes out way ahead on price -- it's not even close.

Thus, I'm very firmly in the camp that says "price" is not the major contributing factor to people eating crap. The two other factors you note, "convenience" and the "picky kid factor" (palatability), are the dominant considerations.