Many factors can influence the price of a product (in general!), but you’ll find that the most common determinant of price when it comes to dog food is the quality of the ingredients used. Alongside this, you can expect to pay more for kibble that is manufactured using special methods.
One example is to compare Orijen dog food — which uses a high proportion of dried, fresh, or frozen meat — with a no-name brand from the supermarket. The supermarket dog food may not mention any specific processes used to retain nutrient integrity, because these aren’t used. Rather, you may find cheaper, but lower-quality processes have been used to keep the kibble edible for longer. Expect synthetic chemical preservatives in the supermarket brand, for instance.
Quality meat and non-meat ingredients are also more expensive than those which can be bought in bulk, often termed ‘fillers’. You will find little to no ‘fillers’ in good quality dog food, such as Orijen. Cliche as it sounds, most of the time you really are paying for quality.