It sells at the $30 range because the minimum price which you can sell to the private market is initially $29. When you have some military tech, demos can bring this up to $36, hence that is the floor price of food.

Basically, food is produced in such plentiful amounts that it will almost always be near $36, rather than the $261 end.

And part of the thing is that based on the current game equations, food at $45 is actually equal income for a casher and a farmer at the same land size (both with appropriate maxed techs, and equal army size). If the equilibrium point was higher, more people would play farmers over cashers, and that would bring the food price down, and vice versa.

As it is, food will average $45 as a consequence of the game equations, going above and below it in equal measure over the length of a reset.