If there's one myth that drives dietitians crazy, it's that eating well breaks the bank.

There's this belief that healthy groceries are expensive, but that's not always accurate," says Tami Ross, R.D., co-author of Diabetes Meals on $7 a Day—or Less! Once you know where to find the bargains, you can fill your cart with heart-healthy foods without blowing your shopping budget, she says.

Rahaf Al Bochi, R.D., agrees. She's a spokesperson for the Academy of Nutrition and Dietetics. "There are so many ways to purchase healthy groceries on a budget," says Al Bochi.

We asked the two dietitians to help us navigate the aisles with savings in mind. Here's what they recommend.

Make your diet whole

If processed foods seem cheaper than their whole-food counterparts, it's probably because they're often small portions in big packages. An 8-ounce bag of potato chips, for instance, is roughly the same size as a 5-pound bag of potatoes. It costs about the same, too. But do the math: 5 pounds is 80 ounces, so in this case, the processed option costs about 10 times as much. And for that upcharge, you receive a glut of cheap processing fats that you'd probably never use at home.

That rule holds with all processed foods: Every time somebody (or some machine, in most cases) peels, chops, or flash-fries your food, the sticker price goes up.

Ross points to carrots as another example: Many stores sell them shredded. But a quick scan at a local supermarket turns up a 1-pound bag of whole carrots for 88 cents, while a 10-ounce bag of the shredded stuff costs $1.99. It's the same food with a 127% upcharge for shredding! "Get the whole carrots and shred them yourself," says Ross.

Other major whole-food health bargains include uncooked whole grains, unflavored oatmeal, and raw nuts (which tend to be cheaper if you buy them from the baking aisle). Yes, these foods require some preparation in your kitchen. But they save you money without sacrificing health.

One exception to the processed-food rule is with frozen produce. Ross recommends passing through the freezer aisle to find fruits and vegetables that sometimes cost less than their fresh counterparts. Frozen food is less likely to spoil and go to waste, and it can be more nutritious. A study from the University of Georgia found that some frozen produce provided higher nutrient levels than fresh-stored produce. Frozen green beans, for example, contained 40% more provitamin A than beans that had been stored in the fridge.

Go big—or very small

Midsize grocers often have the highest prices. So one strategy is to target massive retailers that offer bulk pricing. "You could save significantly by shopping at supercenters and warehouse clubs," says Ross.

But don't limit yourself to the big guys. On the other end of the grocery spectrum, you have the local farmers markets and co-ops, which eliminate the middlemen who drive up prices. "Often [local markets] have produce at a much lower price point than chain grocery stores, especially at the height of the season," Al Bochi says.

Not everything at the farmers market is less expensive, but a study from the USDA's Agricultural Marketing Service and the Vermont Agency of Agriculture, Food & Markets found that the prices were competitive with those found at grocery stores. And for some vegetables, your local farmer has the price advantage. In the study, farmers market zucchini cost $2.90 per pound, versus $4.49 at the supermarket. Other farmers market bargains include tomatoes, garlic, and summer squash.

In addition to saving you money, farmers markets and co-ops can introduce you to new fruits and vegetables. You might even pick up some new cooking tips: Local markets often provide recipes and preparation ideas for the in-season produce they offer.

One final bit of advice on where to shop: If you're an impulse buyer, consider buying online, says Ross. Curbside grocery pickup programs and delivery services sometimes charge a small fee, but if you're prone to making unhealthy decisions in the aisles, the benefits can outweigh the costs. You can purchase only the things you need without giving in to frozen pizzas and candy bars. "Plus, you can take advantage of online specials that may not be available to those shopping in the store," Ross says.

Break out of your meat rut

As we age, it becomes increasingly important to take in adequate amounts of protein. But meat is one of the supermarket's most expensive food categories. So what's the solution? Home in on meatless sources of protein, says Al Bochi.

She's not talking about tofu and protein shakes, although those are fine options. Instead, she means foods you probably already eat: Eggs, milk, Greek yogurt, nuts, and cheese. Peanut butter delivers 8 grams of protein per serving. A can of tuna delivers 22 grams, nearly twice as much as standard fast-food hamburger. With more of these foods in your diet, you don't need as much beef, chicken, or pork.

Both Al Bochi and Ross point to dried beans as one of the best bangs for your buck. And our supermarket sleuthing proved their point. On a recent trip, we found 1 pound of ground beef—enough for four servings—for $4.79. Meanwhile, 1 pound of dried black beans sold for $1.39. As it absorbs water in the pot, it will swell up to 13 servings. So on the beef side, you pay $1.20 per serving. For beans, it's 11 cents.

Consider making taco night with beans instead of meat. Same goes for chili: Reduce or eliminate the meat and "beef" it up with beans instead.

The upside to eating less meat goes beyond just reducing your grocery bill. You may also reduce your intake of saturated fat and cholesterol. Who said being cheap wasn't good for you?