Lentil Dahl with basmatti rice, can easily make this on mass for very little money. Plus you can spice it up a bit with some extras like popadoms of home made chutney or something.
Rice is what a £1 a bag? Red Lentils under a £1 a bag, and a jar of vegan curry paste. An onion and some garlic.
Bean farmers pie, kind of like shepherds pie.
Couple of tins of kidney beans, couple of tins of chick peas, couple of carrots, an onion, some garlic, mixed herbs, some potatoes, tomato paste.
Risotto with baked tofu, or with salad.
Risotto rice, onion, garlic, mixed vegetables (peppers, red onion, leaks, mushrooms, baby corn whatever you feel like, Rocket or spinach) firm tofu and tamarri/soy sauce. Pine nuts to toast and top with.
Salad leaves and tomato
Those are a few of my on mass suggestions that shouldn't cost too much to produce.
How about making a vegan cheese cake though with the tofu and cream cheese that could be a bit pricy and possibly time consuming. How about making pancakes and serving with melted vegan chocolate and fresh strawberries or making a vegan chocolate cake? Or flapjacks. I Suggest making some kind of desert just because when people think vegan they never think we eat anything remotely sweet or interesting.
Flapjacks would be cheap, as would chocolate cake, cocoa, flower, sugar, marg, water, and you're there, simple.
If you want any more info let me know.