For the level of processing involved, marijuana isn't that cheep when compared to any other bulk farming product. Hemp fiber for example is around $150 per ton. The markup is still very high comparatively for the drug product.

When you look at the production line of something like high fructose corn syurp, you could industrialize the process in to the range of $10000 per ton pretty easily.

Again, it's the black market that turns it into the million dollar range because of the risks involved.