If you buy pasta, 200g of lardons (I've found that they're cheaper and tastier at Intermarché with their "ranou" brand) and 250g or 250cl heavy cream, you can have a "carbonara" for roughly 5€ that will last you for 3 days, for lunch and dinner, with a full plate and little energy spent to cook it.

What unsettles me the most is the absence of substantial quantities in your plate, wanting to eat in a healthy way is good, but if you struggle financially, eating is what must come first. Pasta or rice is rather cheap while being fulfilling, and you can combine them with small other stuff for taste and calories in a full plate.

Your body and brain will thank you way more to have full plates than a carrot with almost nothing else, and during your studies the brain needs to be working smoothly.