Are nutritous school lunches much more costly than junk food?

Sometimes I just can't understand why many public schools can't have a healthy school lunch menu at least 74% of the time. I've seen some schools that have made very decent strides towards a healthy school lunch menu, while others serve cheeseburgers, fries, milkshakes, fried pies and other unhealthy items several times a week.

Either is it much tougher financially to actually provide semi-healthy or healthy meals to public schools or something else is going on here. Although there are standard-of-living differences all over the map in the U.S. for families,California school nutrition professionals are seeking federal funding that indexes both reimbursement rates and free and reduced-price eligibility guidelines to get the state's higher cost of living mapped out as a large variable in the march towards healthier school lunches.

It's not that kids need to eat (or that their palates can be made to accept) organic vegetarian diets at school -- but some semblance of healthy dietary habits would be a good start.