I'm afraid I simply have to comment. There has been so much misinformation and half truths posted here. To qualify my opinion, I currently run a small rescue centre, breed Devon rex cats and have been heavily involved with animals for the last 35 years. All pet food HAS to be fit for human consumption, so the poster who mentioned diseased animals etc is under a iapprehension. Sure it might contain eyeballs, ligaments, cartilage etc but still fit for human consumption. By another name these ingredients are called 'sausages'. Cat food is more expensive because cats are obligate carnivores, meaning that they MUST have a meat diet and in particular, it has to be muscle meat because muscle meat (i.e. heart) is where the taurine is and cats MUST have taurine or they get very ill. So even whiskas et all, have to have a certain percentage of meat in the can or pouch and that meat needs to be muscle meat. Look at the labels. Check the protein level and the first ingredient. I currently have over 30 cats who, because of financial constraints, eat nothing but dry cat food (kibble) I buy one of the cheaper ones which is called 'breeder pack'.Breeder pack the copany buys up all the end of runs.So, if Whiskas makes 101 tonnes and only has orders for 100 tonnes, and James Wellbeloved has the same, Breeder pack buys up the suprlus and mixes it all together, then analyses the nutritional levels in order to maintain a certain level of protein, ash, oils etc and baggs and sells. The sack I buy this month may have a different look to the ones I biught last ,months because it all depends on which companies had a surplus.All 30+ rescue cats are fit and healthy on this cheaper food. As far as kibble goes, dog or cat kibble, expensive or cheap, they are ALL grain based, so don't get sucked in to believe that an expensive one is any better. I have here a cat aged 16 and one of 15 and several aged over 8 years, all fed the same, all fit and healthy. Occasionally someone donates a couple of sacks of something fiendishly expensive and I have not honestly noticed any different in stool quality, coat shine or anything else when the cats eat the expensive stuff. Be guided by your cats. If mine get really cheap stuff from say ALDI or LIDL, I find they puke it up. So I just don't buy those. If you find a brand that your cat likes, that it does well on and that you can afford, then stick with that one even if the brand snobs look down their noses at you and make you feel as though you are an animal abuser.
Dog food is a different thing again and I'll happily explain the why's and wherefores if anyone is interested. I not only run the rescue but am a dog behaviourist and run a free advice line. I keep a veritable menagerie of domemstic pets, exotic pets and livestock so should be able to give sound advice based on actual experience and common sense, as opposed to something I heard of someone who heard from someone else, and things I believe without actually knowing for sure.