A large bag is cheaper per gram only if you can store and use it. An ingredient that sits untouched is not a bargain because its unit price was low.
Build meals around foods you enjoy and can prepare with the equipment you have. Canned beans may cost more than dried but save time and fuel; dried beans can be useful when your routine supports cooking them safely. Neither choice wins in every kitchen.
Use overlapping ingredients and plan a flexible meal for safe leftovers. Compare drained weights where relevant and avoid buying several substitutes before tasting one.
Keep an eye on the expensive extras: sauces, toppings, and specialist snacks can add more to a basket than the main ingredients. A simple meal does not need every optional garnish listed beneath the recipe.