A jar of bolognese sauce (the first one Google brought up, a well-known brand definitely not 70p) contains tomatoes, tomato puree, onion, sugar, starch, sunflower oil, a few herbs, citric acid and garlic.
So no meat yet, no pancetta, no carrots, no celery, no wine stock, nothing sundried, no bay leaf, herbs so few they're barely mentioned at the end, no cheese, no pasta, no garlic bread. You'd have to add all these.
Now let's go for a basic version:
Reconstituted Tomato Pureé (48%), Water, Tomatoes (5.7%), Modified Maize Starch, Salt, Vegetable Oil, Sugar, Citric Acid, Garlic Powder, Black Pepper, Dried Basil, Dried Oregano
Essentially, half tomato puree half water.
Do you think if you cooked like that you might end up spending a lot less money?