In
most cases you get what you pay for. Cheaper foods often use cheap ingredients,and most often than not have grains/cereals as the first and predominant ingredient and very little meat and of poor quality,labelled as derivatives and by-products.
You can also get expensive poor quality food,such as the brand often found at your vets office ;)
I prefer to feed high protein,high meat,no/low grain dry foods. My favourite is Orijen.
If price isnt a factor check it out along with Timberwolf and solid Gold at
http://www.zooplus.co.uk/shop/dogs/dry_dog_food/orijen/44954 They also have other decent foods.