This post is for ETH students who have strict budget constrains.
Before going into the details, two meta-comments.
First, I never felt comfortable sharing these details. Nevertheless, my past self (almost 7 years ago) would find it useful.
Second, if you can work on the side (even 1 day/week — especially in CS), that may be enough to give you more room in your budget.
Youth hostel / AirBnB / friends.
This is needed until you find a more permanent place of stay, and sometimes that may take a while (2-3 weeks until you move to your permanent place).
If you see a listing about a room in an apartment that is not rented for a while, you may contact the owner and ask if you can stay for few days by paying pro rata. This is useful if at some point (usually weekend) the Youth hostel is fully booked. I never tried the AirBnB/friends solutions because they were not available.
Food: If you can’t cook at the temporary place, you can take the precooked chicken. You can clean your hands with wet wipes afterwards.
Try student housing.
Alternatively: Find two more people. The goal is to find an apartment in a building that is going to be renovated/demolished after ~6 months. You can find an apartment that can host 3 people with a price around 1000 francs. This is usually too expensive for 1 student, and too bothersome for a family to move out again after few months.
Using wohnen.etzh.ch you have good chances of getting accepted for the apartment.
Go to a German supermarket (Aldi, Lidl) once per week. Budget around 50 francs. Look at the price per kilo and not per item.Avoid food that costs more than 10 francs/kilo. Pasta/rice/chicken/pizza/Paella/toast/sausages can be cheap. Buy fish cans with different sauces that you can use it on pasta/rice so you don’t get bored of eating the same thing. Don’t eat at Mensa. Eat at home or take food from home with you.
On Saturday mornings on Helvetiaplatz you may find second hand clothes very cheap. Once, I bought a pair of jeans that were only 2 francs. Otherwise, try Brockenhaus.
Buy a second hand bike. Put in your backpack extra clothes. Have waterproof jacker, pants, gloves, shoe covers. Don’t repair your bike once it is broken. Buy a second one around 100 francs after 4-5 months, if the first one is broken. Use the materials from the first one as replacement for the second one. Even without that, it is cheaper than public transportation (amortized).
Alternatively, if you don’t like biking in the rain, get a Halbtax and a Gleis-7 card. Check the weather prediction every morning. It rains about twice per week in Zurich. If you return after 19.00 by train, you will have to pay only the 1-hour ticket to go to ETH.
Initially, buy cheap furniture for all people together. Share transportation costs. When you move to your second apartment, rent a big car. Do the cleaning yourself carefully. It takes at least a day. One more day for the move.
Go to parks, friends places’. Invite friends. Spend time at ETH.
Get an exception if you have a health insurance in your home country. Otherwise, find the cheap insurance for students. Go to the dentist/do checkups in your home country.
Book well in advance for Christmas. It may be more convenient to have your roundtrip flights starting from Zurich, but usually it is cheaper the other way around.
Get the cheapest option. Call home through internet. If your parents do not use a chatting app, you can always buy credits on Hangouts/Skype.
Check if someone from a neighbouring apartment wants to share their connection. Refer your friends/other students and get a referral from someone.
Some costs are not recurring (e.g. clothes, bike, moving out, airplane tickets). Budget for those.
Try an internship or a part time job even at ETH — ask your advisor. Check the regulations. You can work during summer/exam period as much as you want. During the semester, 2 days per week.
Check the guide from ETH. Ask other students. Focus on your studies. You are not alone.