Just because some study says that eating healthy is too expensive, does not mean that it is sound advice. Consider the fact that food is the very fuel that our human bodies run on. The quality always affects the outcome.
The cost of poor eating is your health. All the money in the world doesn't matter, if you are ill.
As a nutritionist, I have noticed that the very same people that say they can't afford healthy food are more than willing to drop 4$ for a latte or 10$ for a drink at a bar. It really comes down to priorities.
We've been fooled into thinking that food should be dirt cheap. If it's really a concern, then join a buying club, CSA (community supported agriculture), grow veggies in your yard, or check out deal at your local farmers market or co-op.