How much does a portion of cheap vegan food cost approximately?

I would like to calculate roughly how expensive a portion of simple vegan/vegetarian food is when cooking for a lot of people. Sometimes it's about 20-30 portions, sometimes 50-60. It's about dishes like chili sin carne, pasta with pesto, pasta with vegetable bolo, vegetable curry with rice, potatoes with curd cheese. Is €3.50 too low…