Housing Aid that You Didn't Know Existed
I didn't know that this existed until I arrived, but it changed everything. My entire housing budget was changed. I started in a dorm room with 6 girls and it was terrible. I couldn't sleep, but I thought that it was all I could afford, until I heard about the CAF. It is housing aid (but to be eligible you must be under 26). When you arrive you must create an account. It has been a while since I did it, but when you go to the site I believe its under "services en ligne" and "faire une demande." Make sure to fill everything out and upload all of the supporting documents, like your visa and bank account info, etc. Once that is all done you will get approved for a certain amount. Personally, I receive 207€ a month. You will pay your rent as usual and on the 5th of each month you will be reimbursed by the caf for up to 207€ I believe.
The important part is to do the "demande" as soon as you arrive, because you are only eligible starting from the second month you are here. As long as you have done your "demande" you will be eligible starting from the month after you've done it, even if you don't submit all of the documents at first.
For example, I was confused about how it worked and I had to mail some documents in after I created the account, they requested certain documents like a translated birth certificate, which I didn't have. So I had to get this first. I did the request in September, so I was eligible from October onwards, but didn't end up sending the documents in until February. March 5th, I received my first payment of around 1000€ since I was eligible for October, November, December, January and February, they reimbursed me all at once. Usually of course you'll only be reimbursed for one month at a time, since on the 5th its always the reimbursement of the previous month, if that makes sense. Of course I recommend getting all of the paperwork taken care of early on, but its not crucial. The important part is that you start the "demande" when you arrive.
I also have recently discovered another aid for up to 100€ a month. This is only for those of you en alternance (so this will probably be during your second year of masters). But it's the Aide Mobili-Jeune. It's very similar to the CAF. You go to their site, sign up, up load the supporting documents, and wait. I think its a bit simpler than the CAF, but I haven't received the aid yet since I just did the demande, so I will keep you guys up to date on how it turns out haha.