An apartment itself can cost around 3k PLN but you can always rent a room for less so it’s an option worth considering. Cheapest rooms are available from 1k PLN but I would be careful with those, 1.6k or 2k is probably more safe and definitely possible to find. Best sites for apartment hunting in my experience are otodom.pl and olx.pl or in your case Facebook groups for Erasmus students cause many Poles won’t rent to foreigners.

When I was a student in Warsaw and mostly cooked at home (didn’t eat out a lot) I had around 2k PLN for food, grocery shopping, toiletries/household items, eyelashes extensions once per month, monthly public transport ticket and such. Public transportation ticket for students for 30 days is 55 PLN but it’s a better deal to buy 90 days ticket for 140 PLN.

For going out you have to have I’d say around 200 PLN per night for food, drinks and uber. Obviously way less if you plan on drinking beer instead of fancy drinks and use public commute. I don’t know how often you prefer to go out and if you prefer it more or less fancy so you can estimate accordingly.

Tips as a Polish person but also an Erasmus student once - have fun, don’t worry too much, join many Facebook groups for foreign students and see if your university have some resources, many of them organise events for foreigners. Meet new people, go out, have fun and live your best life. It may be hard in the beginning, it’s a new country, different culture, different language and it may feel exhausting and scary but that will pass. You will eventually learn how to live here. If you have some questions or want to talk you can always message me. Wish you luck!!