When my dog was a puppy he was raised purely on Science Diet Large Breed Puppy dry food (and our leftovers). It has a high corn content which isn't good for Dobermans but when we switched over to Royal Canin we found that his pee was burning our grass so we changed back to Science Diet. We would buy the 15kg bags which cost us about $120 - $140 and would last a month.
Now he is 17 months old and we feed him Royal Canin Energy for Adults and it's around about the same price. We feed him about 3/4 his serving size and give him 4 - 5 frozen chicken necks and our dinner leftovers as well. If we give him brisket bones through the day he only gets half his serving size, 2 chicken necks and leftovers. Twice a week when we have roast dinners he doesn't get anything but leftovers as he gets half a chicken, heaps of roast veggies and sometimes if he's lucky he gets gravy as well... We love our gravy so usually there's none leftover haha.
We opted not to feed him supermarket brands. We might change once he's finished developing, when that comes I would go with Purina Supercoat Adult Large Breed which I believe sells for $24 for the 18 kg bag. Huge price difference but worth it imo.