Do you know where you want to work? There are big chain school like Empik, Speak Up, Profi-Lingua and IH in many cities. Average pay is about ! Zloty a minute, which is $18 minus 20% tax. So, if you do 20 hours a week, you'll make 20x60=1,200 minus tax or 960Zl, which is just shy of $1,200 a month. At Profi-Lingua you can make more than this by doing extra hours but IH pay well below this. The average language school deal is less than 3,000PLN plus accommodation. In the summer, you will be laid off for 3 months.
What you should know is that Poland is no longer cheap. It costs more there than the USA for many things, so the question you have to ask yourself/yourselves is could I/we live well on those figures? Rent will gobble up $5-600, mobiles are expensive to run and petrol is about$1.70 a litre. Clothes and electronic goods are expensive and the former are often of poor quality. Supermarkets are cheap but eating out is costly if street food is not your thing. Travelling around can be done cheaply if you stay in hostels but hotels can be a right con. Bars are cheap if you stick to beer and Polish vodka but other drinks can be really steep, especially single malts.
On a positive note there are lots of nice cities, forests, lakes and mountains to see.
Tips on living cheaply include; getting a monthly tram pass, using Skype, avoiding taxis, shopping in Tesco and street markets, sticking to Polish drinks, looking on Gumtree for a flat, buying your winter jacket, clothes and boots stateside, eating pork, chicken, Polish kielbasa and spuds. Also watch out for thieves. I've lost several mobiles there.