Minimum wage is 1,386 Polish złotych per month (523. U.S. dollars).
I also worked in a supermarket for 1$ per h,
1$ is 2.6 Polish zloty which is not what most people earn, even on the black.
I think you may have your dollar to zloty exchange rates mixed up.
students don't pay taxes so they get more money
This is true, educated and skilled work force = WIN!