But i checked few classifieds website of Warsaw and i found that there are some offers for 2 room flat or 2 room shares for 1300 PLN (650 per person) + fees.
That's about 1700 to 1900 PLN with utilities and fees, so about 850 to 950 per person, and way below market value. Expect there to be serious problems with the apartment (very hard to get to the city center, bad building or neighborhood, very small rooms, poor condition, reeks of cat urine, cockroaches, extremely small "kitchen annex" that is essentially useless for cooking, microscopic bathroom, bad windows (means heating is going to be VERY expensive), dampness and mold, or something else major). Another problem that you may have, which is very important for you, is that the landlord may not permit you to register your address there.
For example, one place I checked out that was unusually cheap turned out to be an apartment built over a car alarm shop, next to the main railroad tracks in a rundown part of town with poor access to the city center. Not exactly a good place to study. Another was in a building that reeked so bad of cat urine that I almost vomited when I went in. Another had rooms so small that there was no way to fit both a bed and a desk in them. Yet another was so far out I might as well have been living in a different city.
For your own room, like I said, the cheapest you're going to pay is 600 PLN for a VERY TINY room in a student apartment, to 1500 PLN in a two-bedroom apartment.
My advice is not to even waste your time checking out these unusully cheap places.
As for fees and utilities, it depends a lot on the heating and building association fees, but expect to pay 300 to 400 PLN per person, and 500 to 700 per two persons, plus or minus, over the rent price you see in the . Bad windows could double that, so have someone competent check out the place for you amd make sure it's OK before signing anything.
Also, remember that, in Poland, a two room apartment means only one bedroom.