Eat seasonal fruit & veg & make seasonal salads eg use shredded cabbage & chopped apple/orange & dried fruit in the autumn & winter: far more nutritious, tastier & better value than out-of-season lettuce, tomatoes & cucumber. You could also get a salad sprouter & make your own beansprouts etc, which are especially good for winter salads.
I agree that chunky soups are a great way of eating healthily & cheaply, & you can make them into a main course by the use of pulses & filling but healthy root veg in the winter (& maybe rice & a bit of curry powder for mulligatawny) or things like fresh toms, carrots & courgettes + potatoes in the summer (add pasta for minestrone or pesto & green beans for pistou).
I have (vegetarian) cookbooks by people such as Rose Elliot & Gail Duff that I've had for years, which have loads of cheap & wholesome but interesting recipes, & once you get into it, you can make up your own combinations of soups/salads/stews etc.
I agree that Indian food gives lots of opportunities for cheap meals, & tofu is full of nutritional value & not expensive, just needs marinating eg in soy sauce & fresh ginger for stir fry. Ring the changes with different grains: if you have a good wholefood shop they're likely to stock a lot of variety including things such as unusual grains & non-wheat-based pasta, & you could eat it with a chunky tomato sauce (use fresh in summer, tinned in winter) or mushroomy sauce.
Then there's things like veggie frankfurters that are very versatile: our children like them just with veg & pots, or to make them go further you can put them in a German-style lentil soup, chopped up with pasta or in a salad.
Then there's Quorn or TVP mince, which are both healthier than beef mince & form the basis of nutritious traditional meals such as shepherd's pie & chilli con/?sin carne.
If you don't have one already, a bread machine could be a good thing to put on your Christmas list as you could save loads of money by making your own wheat-free loaves. They always come with recipe books, & along with many others I recommend the Panasonic.