Generally speaking, the higher priced food mean that the ingredients in the food are higher quality. Realize though that big companies that do a lot of advertising of their foods also have to pay for that with the proceeds from their sales, so sometimes price skews things a bit as well and higher price can mean lower quality.
Overall- if you can buy the food at a grocery store (Purina) or mega store (Eukanuba), it's not the best for your dog. It's better to buy foods from stores that specialize in pets. I personally buy my dog's food from a store that makes a living selling only dog and cat food and not pet supplies as well because the staff knows the foods very well and can help me if I need to make a switch. Since the owner of the store also has pets that are eating the food she stocks and her staff does as well, they all know the products very well and have a vested interest in keeping things fresh and up to date. Pretty much any food in that store I could feed my dogs and not worry too much about the quality. Also, because i'm feeding such a high quality food that gets utilized well, I don't feed my dog's as much as some of the lesser quality brands.
Go to this link if you want to learn more. Ask more questions if this is confusing- it really can get complicated depending on one's beliefs etc.
www.dogaware.com
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Chelle and the rest of the crew including, but not limited to Kita and Taiko (the shiba inu wrestle maniacs), Adi (reserved and dignified tabby cat), and all 28 reptiles