The cheapest fruits and vegetables are the one’s you grow yourself (we’re working on it). A secondary choice for the more social and enterprising kind is to ask people if you can come and pick it off their lawn or trees in exchange for, say, half the loot. For the less enterprising, I suggest loss leaders. A loss leader is a product that a supermarket sells at a loss in the hope that customers buy more expensive things.
The traditional way is to keep a price diary of various produce. When something drops substantially in price, you know what the main ingredient of this week’s meal is. Buy for several days and design recipes around it.
As always the most important thing when it comes to saving money on food is learning how to cook. What ingredients can be left out, which can be substituted for others, etc. If you don’t know how to do this, you’re part of the reason why loss leaders work (from the seller’s point of view).
Suppose you don’t have a price diary. In that case pick up some junk mail and see what’s on sale this week. Alternatively, get on the supermarket’s website. This list can be cross-correlated
with a list of what is grown locally and is in season currently. Those are usually cheaper already. Besides, it’s ecologically sounder and better karma not to have strawberries shipped in from New Zealand in January. A third way is the local farmer’s market. Unfortunately around here that seems to be targeted at rich yuppies and is priced accordingly.