The answer is supply vs. demand.
An orange is more expensive in the United States because a delicious, juicy, navel orange can command a price of $1USD each. The American consumer will pay that much for one and the grocery store knows it and the orange suppliers know it. An orange does not cost the equivalent of $1USD (27 Cuban pesos) in Cuba because it would not sell at that price, the crop would rot, the grocery store would not purchase the orange from the supplier at that cost, and the orange supplier could not sell its crop.