There's no denying that meat — and good-quality meat, which is the only kind you'll really want to eat — is expensive. You can get plenty of protein and low-fat fibre from pulses instead.
If you already do meat-free Mondays, why not try extending that vegetarian diet to more days? There are lots of swaps you can make using tofu, Quorn, and other meat substitutes too. Just make sure you're still meeting your nutritional requirements.
Comparison: While Sainsbury's Beef Mince 5% Fat (500g) costs you £3.50, a tin of Sainsbury's Basics Red Kidney Beans costs just 10 percent of that at 35p.
You could use those beans in your bolognese instead of the mince. You don't have to go the whole hog — you could just use half as much meat and bulk out your meal with pulses.