Cucumbers, onions, radishes, tomatoes, chilie peppers, and herbs can add up quickly in a store, but all produce heavily and and easily with a small initial investment. Reuse pots from last years annuals, add a layer of compost and some fertilizer, and plant on plant per pot. Each year, add a pot, or make a "raised" bed.
[An] example of a vegetable that could yield big savings is tomatoes, says Greenberg. “Tomatoes can cost $2 to $5 per pound,” he says.
“A seed packet costs about $3 and can easily produce a harvest of 25 to 50 pounds.” - The Allstate Blog