Good ones that are good value are Carny, Bozita and Smilla. There's also Feringa, which is a little more expensive, but not much. Those are all cans and you can also get Bozita in tetrapacks and the food looks different, but it's still decent.
These do work out cheaper than Sheba as the higher meat content means they don't eat so much. One of them has a recommended feeding amount of around 160-180 g per day, which is just under half a tin, so you might get away with 4-5 tins a day between the lot of them.
Some of the above also come in 800 g tins, which you could use when feeding so many cats, but I've used those (we foster and have 4 of our own, so have a minimum of 4 up to about a dozen to feed) but I find the 800 g tins quite difficult to handle (small hands).
You could also try them on some or all dry food because even the ones that appear expensive are quite economical to feed as, again, they don't eat very much of it, as long as you don't have a greedy sod, who hoovers it up by the pile - some neutered males are known for this.