Even if you have to pay ZUS 7000 Gross pr. month will turn out to be 5000 NET.
2000 zt after paying some other stuff and send money home
I wouldn't advice you to try and send money home.
Money earned in Poland should be spend in Poland due to the prices. Well actually this depend where you send the money too, but in case your from western europe it just wouldn't make sense.
But you can live on 2000zl pr. month. like smurf said not great, but you'll survive.