Minced meat(chicken, beef, lamb) and tripe are either 35p or 65p a lb at my supplier, can’t remember which price but even at 65p it’s still cheap. A kilo of duck necks or chicken wings is also cheap. Add a tray of eggs, some offal and a bag of frozen veg and imo that’s a cheap months feed for a dog! Personally I got a lot further than that with high quality grub but it’s achievable on a budget.
You should get a smallish chest freezer, on a Sunday afternoon hit the supermarket and you’ll find some bargains.