Late to this thread but thought would add my tuppence worth regarding cheaper food...we actually still have Ollie on a puppy/ junior kibble (Chudleys) despite the fact that he is well over 2 now, and we have no intention of moving to an adult food.
To my mind it has the high levels of proteins and nutrients that more expensive brands boast of for adult dogs, despite being a fraction of the cost (approx £18 for 12kg). We feed a smaller amount as it is naturally high calorie and a quite high proportion fat but he maintains a good weight on it as he is very active doing regular 5k runs and swimming most days. Because it has smaller pieces of kibble it is also compatible with most treat dispensers, so he receives his meals in these which entertains him and slows down the rate at which he eats. I think foods that describe themselves as suitable for pups have to meet a higher standard so we're happy and I would estimate it costs about 22p a day to feed.