Good quality food doesn't always cost more. For example, hi life essentials actually costs less at Asda for a box of 12 pouches than the likes of Felix and Whiskas. Yet it has a much higher meat content. Of course, not all cats will eat it and not everyone has an Asda nearby, but it just illustrates the point that it isn't always a case of not being able to afford good quality food. It's more than likely a case of not knowing the difference. Lets face it, most people dont' read the labels on their own food, let alone the cat food they buy.
You can get good quality food in supermarkets. Sainsburys sell Encore and hi life as mentioned (and they do some foil tray stuff in their own range which has something like 14% meat rather than the 4% in whiskas, felix et al). Tesco sells tesco luxury and tesco finest as well as the foil trays of just nature. Asda sell the hi life essentials pouches 12 for £2.88 and the small tins at 4 for £1. And as mentioned, Asda sell hi life essentials which is a very cost effective yet high quality food.
Dry food wise there's Joe and Jill's in Sainsburys (and Tesco?) and most sell Purina One which is better quality than many supermarket brands. Wilkinsons well hi life dry.
re raw - I don't feed a raw diet, but I do give raw meat as snacks. Jaffa has raw chicken wings a couple of times a week and they both get pieces of raw meat as snacks quite regularly. Jaffa absolutely loves it and will cope with large pieces despite the fact that he'd never really had anything like that before the age of about 10! Mosi who is only 3 likes his pieces small but he is getting better and will now eat pieces that require a fair bit of chewing/tearing apart.