
The best cheap supermarket food is without a shadow of a doubt Butcher's Classic. That has 49 % meat compared to the 4 % of most other supermarket cans. You can usually get a pack of 12 cans on special offer for £5 so it's extremely good value.
The Natures Menu pouches are excellent, over 70 % meat, but of course work out a lot more expensive, especially depending on where they are bought etc. I get them together with my mince order on a breeder account with a discount and end up paying roughly 50 p per pouch.
Natures Menu also does a complete raw frozen food for cats, that is quite seriously expensive but there's no doubting the quality. Likewise Natural Instinct is good but very expensive indeed. Also Applaws cans or pouches, superb quality (you're talking over 90 % pure meat) but expensive.
Personally I'd be happy with any of these or indeed a mixture -for instance using Classic as well as one of the higher meat content expensive ones can make it a bit cheaper in the long run, and Classic is easier to get hold of.