/ Costs of living in Bialystok
Please ignore what dominic is saying, he runs to all these types of threads and spams them, not sure if he's some ultra nationalist that doesn't want outsiders in Poland or whatever but I just got back from there, my sister and her husband live an hour away from Warsaw, they have 2 kids and only make 4500zl after taxes and they live quite well.
The average income after tax in Warsaw is around 3750 PLN, or approximately $850 USD per month. This figure shows how Warsaw is a wealthy city not only in the national economic sphere, but also regionally. In other important cities of Poland, the average salary is considerably lower, including Krakow or Wroclaw.
otodom.pl/oferta/komfortowa-szeregowka-do-wynajecia-ID3keFa.html#gallery  Full house with 3 bedrooms in the city = 2800zl.
rent will be your biggest expense, rule of thumb is if you want a comfortable life you will spend as much as your rent in expenses/month.
Dominic is over the top when he talks about savings, I'm guessing he's a multi-millionaire now after reading his wild posts. From what I've seen in real life most people don't save much in there savings account whether here in Canada or there in Poland. Usually savings come from real estate, when you buy & pay off your property plus the % it grows over 20 or so years usually pays for your retirement. But 90% of the time people don't start making big money from work or other ventures until they get older and wiser, between 40-60yrs old is the magic number when people begin to understand the world and really generate large sums of cash with moderate effort, at least that's what I've seen.
So to sum up, you will need 5600zl/month lets say 6,000zl for good measure. This is of course after taxes.