The chart was put together by the Physicians Committee for Responsible Medicine, but its figures still, alas, look quite relevant. Thanks to lobbying, Congress chooses to subsidize foods that we’re supposed to eat less of.
Of course, there are surely other reasons why burgers are cheaper than salads. These might include production costs, since harvesting apples is probably more naturally seasonal than slaughtering cows (even though both are in demand year-round). Transportation and storage costs might also play a role, as it’s probably easier to keep ground beef fresh and edible for extended periods of time, by freezing it, than cucumbers.
Whatever the cause of the pricing change, there is little doubt that many healthful foods have gotten much more expensive relative to unhealthful ones.