Yeah, there is affordable food out there of almost every type, but as a whole, the cheaper stuff tends towards the unhealthy side. At that point, it's a simple numbers game, in the long term, the cheapest stuff will be purchased more often.
Another thing that has been ignored in this thread is that a lot of the healthy foods mentioned are stuff that doesn't have too long of a shelf life. These fruits and vegetables are going to spoil a lot quicker than that bag of chips. Yes, there are ways around this, but it definitely factors in, especially when we're talking about the money issues.