Nobody knows the real average salary in Poland. The government's statistics office is calculating average only based on reports from businesses with >10 employees (IIRC). This excludes a couple millions of microbusinesses and of course the biggest employer in the country, aka the state itself (millions of teachers, policemen, soldiers, all the paper-pushers in various parts of bureaucracy etc. etc. are not included). The computed national averages are good for comparing year-to-year salary growths, but they're not informative w.r.t. absolute salary levels.

It's really not that much. Rent will consume a half of that right away.