Trying to think of stuff from my student days:-
Any thing with mince, and beleive it or not Quorn mince is good and cheap.
Spag Bog
Lasagne
Cannelloni
The advantage with these three being that you can make one pot of the same sause and turn it into two different meals.
Sheperds Pie
Mince and potatoes (squirt ketchup into the sauce, makes it less boring)
Meat balls
Cheesy white sauce with everything it it. My mums famous leftovers meal, nice with rice. She tends to put chicken, boiled egg and some sort of veg through it. Very cheap.
Anything with eggs. By them in bulk at market/local farmer - omlette, flan, quiche, etc
Tuna casserole
Soups - add pulses to bulk out.
Try to grow your own herbs. Cheaper and tastes nicer than the dried ones.
Curry, particularly veggie curry goes a long way cheaply. Add paneer cheese for protein, and you can make your own by boiling milk and adding lemon juice. (kids love the process)
Roast a large, cheap frozen chicken, and you can make loads of meals out of it and soup/stock with the bones and left overs.
Anyway, hope this helps.