In the pilot of Firefly, Book uses fresh strawberries as part of his transport payment.
The "Mighty fine shindig" has unadorned fresh fruit, showing that it was considered fancy by itself, though Persephone wasn't the most civilized of worlds.
A guilt-ridden Jayne would later go on to buy apples for the crew, which was portrayed as very generous.
This shows that fresh produce is rare and expensive in the world of Firefly, at least to non-Core citizens.
Is it ever shown exactly how rare it is, or whether or not they're also rare in the Core?