This is just wrong. Beans and rice are more than an order of magnitude cheaper than McDonald's per calorie and they're non-perishable. Combine that with whatever fruit and veg is affordable fresh or frozen, a bit of cheap seasoning, and you're still coming out ahead.

You obviously need access to cooking and storage facilities to eat like this, but the target audience of McDonald's is the time-poor, the resource-constrained, or the depressed and disabled, rather than just the money-poor.