If you are a student in Helsinki you can eat at Unicafé quite cheap. Just 2,60€ for main dish, salad, bread and drink.
There are several "restaurants" where you can get the food provided by Unicafé, also in Espoo and Vantaa. Check out the website www.unicafe.fi to get the daily menu in the single locations.
If you like legumes, that this is the right choice for you. But if you expect that the dish called "vegetable temptation" is full of temptation, you will be disappointed. Proper food to stuff yourself, but nothing for gourmets.