Cheaper brands use less protein and more cereal type fillers in their foods. And usually more fat. Dogs need a certain amount of protein to be healthy. I'm not one for buying the high priced dog foods but looked into one that I felt was better quality than the cheap stuff. I finally settled on Pedigree. I can get a 52 lb bag at Sam's Club for less the $25., it's packed with good nutrition and all three of my dogs eat it well. They all have nice shiny coats and are all healthy. I have a chocolate lab, a German shepard mix and a Papillion and all of them are doing great on it.
Now for puppies, you really need a good quality dog food, just like feeding human babies formula. Read the information on the packages and I bet you can settle on a brand that won't cost you an arm and a leg. Better food now means a healthier adult dog.