To see why Twinkies are cheap and fresh produce is expensive,”you need look no farther than the farm bill,” according to this article in the New York Times:

This resolutely unglamorous and head-hurtingly complicated piece of legislation, which comes around roughly every five years and is about to do so again, sets the rules for the American food system — indeed, to a considerable extent, for the world’s food system. Among other things, it determines which crops will be subsidized and which will not, and in the case of the carrot and the Twinkie, the farm bill as currently written offers a lot more support to the cake than to the root. Like most processed foods, the Twinkie is basically a clever arrangement of carbohydrates and fats teased out of corn, soybeans and wheat — three of the five commodity crops that the farm bill supports, to the tune of some $25 billion a year. (Rice and cotton are the others.) For the last several decades — indeed, for about as long as the American waistline has been ballooning — U.S. agricultural policy has been designed in such a way as to promote the overproduction of these five commodities, especially corn and soy.

That’s because the current farm bill helps commodity farmers by cutting them a check based on how many bushels they can grow, rather than, say, by supporting prices and limiting production, as farm bills once did. The result? A food system awash in added sugars (derived from corn) and added fats (derived mainly from soy), as well as dirt-cheap meat and milk (derived from both). By comparison, the farm bill does almost nothing to support farmers growing fresh produce. A result of these policy choices is on stark display in your supermarket, where the real price of fruits and vegetables between 1985 and 2000 increased by nearly 40 percent while the real price of soft drinks (a k a liquid corn) declined by 23 percent. The reason the least healthful calories in the supermarket are the cheapest is that those are the ones the farm bill encourages farmers to grow.

the nation’s agricultural policies operate at cross-purposes with its public-health objectives. And the subsidies are only part of the problem. The farm bill helps determine what sort of food your children will have for lunch in school tomorrow. The school-lunch program began at a time when the public-health problem of America’s children was undernourishment, so feeding surplus agricultural commodities to kids seemed like a win-win strategy. Today the problem is overnutrition, but a school lunch lady trying to prepare healthful fresh food is apt to get dinged by U.S.D.A. inspectors for failing to serve enough calories; if she dishes up a lunch that includes chicken nuggets and Tater Tots, however, the inspector smiles and the reimbursements flow. The farm bill essentially treats our children as a human Disposall for all the unhealthful calories that the farm bill has encouraged American farmers to overproduce.

This last point regarding the poor nutrition available to students is one I’ve heard before. 

The most compelling point of this article is that un-nutritious cheap food isn’t just cheap by the machinations of a “free market.”  It’s cheap because government money is subsidizing it.   This disgraceful state of affairs points to a potential solution, however.  The government could (in a rational world) change its ways and start subsidizing healthy food.  This NYT article suggests that the way to turn things around is to enact a new type of farm bill.  With all the politically-tainted money at stake, though, that might be too much to hope for.