I just made a dirt cheap meal for me and my housemate, cos I couldn't be bothered to make anything complex.
You need:
1 clove garlic (5p? The entire bulb is 55p)
1 tin chopped tomatoes (30p)
One small onion (10p)
Pasta (about 40p worth, we buy bulk)
Parmesan to sprinkle on top (fuck all p)
Put the pasta on the boil.
Chop the garlic and onion finely and fry for 2-3 mins. Add the tinned tomatoes. Simmer until the pasta is cooked. Drain pasta, add the sauce.
Takes ten minutes and easily costs under a quid for two people.