Batch cooking saves money, and freeze, so maybe the initial outlay costs a little more, but it can then work out really cheap
dhal is really quite cheap to cook, can freeze, so you can cook 4 meals worth. You can buy polenta and make a load of chapati and freeze to go with it.
spaghetti bolognaise, my DH prefers the unlean mince, and scoops the fat off, he says it tastes better! and it's cheaper. You can use a whole thingy of mince and that can be split into probably 6 or more dinners, and/or can be used to make lasagne for some variety.
Chilli - you can make this with some of the mix from above, or with kidney beans/no mince. One tin of kidney beans, bulked out with veg etc will make perhaps 3 meals. You don't even have to have rice etc with it, just some bread. Or have it on a jacket potato.
Soup. I love soup made with leftover veg, you can get an extra dinner out of leftovers at the end of most weeks in our house by making soup, enough for 2-4 servings. So you can freeze those not used, or have for lunch.
Shop at 5:30-6pm at sainsbos (in my area anyway) when the sell reduced items at silly prices. I have got a good few freezer things there - mash for 50p, ready meals for £1, deserts for not much (as you are allowed to enjoy the food too).
Porridge for breakfast. Might be boring, but it's my favourite brekky so I have it most days. Buy basics/cheap frozen fruit mix and add a handful to the porridge as it cooks for variety/fruit intake.
I also have a suspicion my cat eats from a neighbours house as he is bigger than he should be on what we feed him. So, if you can work that out for your cat, you can stop feeding him completely 