Fruits and vegetable prices were studied in both fresh and processed forms, where "processed includes frozen, canned, and dried vegetables and fruits as well as 100% fruit juice." The study excluded certain fruits and vegetables sold "each" because of the random weights of these items, although certain random-weight items that were shown to be consistent in weight were allowed.
The study showed that while "value-added" produce (e.g. washed, bagged lettuce, precut broccoli) cost significantly more than their counterparts, but that due to waste (e.g. broccoli stems,) some of those costs may not actually amount to savings. (Savvy shoppers know to use vegetable waste in stocks and sauces, in much the same way as bones, etc.) To account for these discrepancies, fruits and vegetable prices were estimated "by edible cup."
The following fresh fruits - in season - were the best value at under 50 cents per edible cup: watermelon, bananas, apples, navel oranges, pears, honeydew melon, plums, nectarines. Interestingly, only two processed fruits were under 50 cents per edible cup (and then just barely:) applesauce and pineapple - only raisins are under 50 cents per edible cup in dried fruits. (Some fruit juices are cheaper, but I'm surprised they're considered "fruit" by the ERS.)
Vegetables are differentiated by per-edible-cup raw, and per-edible-cup cooked. Best value fresh vegetables were - whole carrots, iceberg lettuce, onions, cauliflower heads, celery stalks, baby carrots, romaine lettuce and radishes. Best value in cooked vegetables were potatoes, cabbage, whole carrots, cauliflower heads and sweet potatoes. Many canned vegetables met the benchmark - sauerkraut, sliced carrots, cut green beans, corn, turnip greens, tomatoes, potatoes, mustard greens, green peas, whole green beans - but only frozen kale, french fries, green beans and corn were under 50-cent per edible cup in the frozen category.
Not surprisingly (especially to someone who's been working with them for some time) canned and dried beans and peas are some of the least expensive produce items available. Every type and form of bean tested was well beneath the 50-cent-per-edible-cup benchmark.
The report goes on to aggregate several day's worth of the recommended amount of produce - considering that the USDA suggests 4.5 edible cups' worth of fruits and vegetables, any produce under the 50-cent benchmark will satisfy the requirments for between $2 and $2.50 per day, leaving between $1 and .50 cents for meats, dairy or other foods (the average benefit for SNAP participants is about $3 per person.) Of course, considering that fresh produce is shown to be the least expensive in many cases, this guide is less helpful for those who live in a food desert - but it does offer guidance as to which specific produce items are most cost-effective.