Buy whole chickens, joint them into 2 breasts, 2 thighs, 2 drumsticks, 2 wings and a carcass. Use the carcass to make stock, and then freeze it. Freeze each type of joint in separate bags. Use the breasts, thighs and drumsticks as and when, but save the wings - do this a few times until you have a bag of enough wings to make a meal.
Mince dishes: bolognese (served over shredded lettuce), moussaka (with a topping made from cream, cheese and eggs), shepherd's pie (using swede in place of mash), sheek kebabs, chilli. Use mushrooms to increase bulk.
Think of cheap fish like mackerel, herrings and whiting. Tinned tuna or tuna in pouches. Make sardine paté from mashed up tinned sardines.
Crustless quiches are great - 4 eggs to 250ml cream, handful of grated cheese, add whatever filling you like (salmon and broccoli, bacon bits, mushrooms and peppers etc.). Mix, pour into a pyrex dish, bake at 180 for around 40 mins or until no longer wobbly. Cool, cut into slices, good for snacks on the run.
Think offal. Though slightly higher in carbs than muscle meats, organ meats (liver, kidneys) are cheap and tasty.
Devilled eggs (remove yolk from halved hard boiled egg, mix with some mayo, seasoning and some hot sauce, I like Sriracha best, put yolk mix back into egg half hollows) are better than plain hard boiled eggs because the mayo increases the fat content - not to mention a more interesting taste.
Have a few veggie-based meals, like cauliflower cheese, or aubergine parmigiana, or big flat mushrooms spread with garlic butter, sprinkled with grated Parmesan, and baked until soft. Look for avocados that are discounted cos they're at their sell by date, and make guacamole.
Aldi and Lidl have some great dark chocolate at a good price. Lidl do a 1000g pot of Greek yoghurt too, and also bags of cashews more cheaply than most places (though I prefer brazils).
Ask your butcher (if you're lucky enough to still have one!) for marrow bones 'for the dog' - roast, then make stock from them, great for soups! Also the marrow itself is a bit of a delicacy, if you like that sort of thing (I do!). Greengrocers will often give you a bag of wilting green veggies 'for the guinea pig' if you ask (and I'm not too proud to!) - cut out the good bits and make soup.
Anything that'll go on pasta will also go on shredded lettuce - think carbonara, alfredo, puttanesca etc.
In a couple of months, think about growing your own salad veggies - it can even be done in a window box, very easy - radishes, lettuces etc.
Eek, that was a bit of a long one, but hope it helps!