You just made think of something else that makes a big difference, and does affects the prices of food and medicine - in central and south america the supply chain is much more shorter that in industrialized nations (mo middle people). A couple of examples: perishable transport is short, usually 1 day. Also, I never ever went to a doctor to get basic anti-biotics, I just went to the pharmacy and the pharmacist would recommend and sell based on symptoms.

In the US the amount of fuel and effort to transport materials and food stuffs is amazingly complicated...