i think a number of excellent points have been brought up.
my personal opinion is that you should feed the best that you can afford,
but you need to make an effort to educate what the best that you can afford actually is. most people just look at the price tag on the bag or the price per pound but not at any other factors at all.
so of course they grab the 10 pound bag that costs for example $7 instead of the 7 pound bag that costs $9, but they don't realize that they would have to feed much less of the "more expensive" food, so the bag would last longer.
then we have a large number of "popular" brands that are quite expensive but still crappy quality, but people buy them because of popularity and advertising and think they are buying the best they can buy. they don't realize that the relatively unknown brand right next to it on the shelf could be better quality at the same price.
i'm leaving out the really low-end foods because we all know how much a diference there is between grocery store/drug store/wal mart stuff and at least "middle of the road" foods.
let's look at some examples:
science diet adult maintenance: $33/40 lbs
science diet advanced protection: $42/35 lbs
science diet nature's best chicken: $42/35 lbs
iams chunks adult: $31/40 lbs
pro plan adult chicken & rice: $37/37.5 lbs
purina one chicken & rice: $32/37.5 lbs
nutro natural choice chicken, rice & oatmeal: $33/40 lbs
nutro natural choice ultra adult: $39/35 lbs
eukanuba adult maintenance: $38/40 lbs
royal canin medium adult: $32/35 lbs
canidae all lifestages: $36/40 lbs (seen as low as $28/40 lbs)
artemis holistic adult: $37/35 lbs
natural balance ultra premium: $41/35 lbs
wellness super 5 mix chicken: $38/30 lbs
avoderm adult chicken & rice: $41/40lbs
chicken soup adult: $29/35 lbs
solid gold hund-n-flocken: $38/33 lbs
innova adult regular: $37/33 lbs
eagle pack natural formula: $31/33lbs
eagle pack holistic select chicken: $38/33lbs
the difference in price
on the bag is overall not that high, but once you compare the daily feeding amount and how long a bag lasts, the outcome is totally obvious. i calculated the diference in feeding cost between science diet adult maintenance and canidae once, with average prices, and feeding science diet was around 45% more expensive. scary.