I have been reading with costy of living very low when compared to Other EU nations.
It's lower, but not very low. Some things are cheaper. and some things are the same or even more expensive. Assuming you are single male, renting a basic one-bedroom apartment will set you back 2000 to 2600 PLN a month, rent, administration fees, and utilities all included. More if you expect more comfort, and less if you are satisfied with a studio apartment. Food, household items, clothing and the like will set you back anywhere from 1000 to 3000 PLN a month, depending how often you go out. Then you have to deduct the cost of your travel, relocation, visa and residency permit.
That leaves the rest as either fun money or potential savings.
I have idea of 12k-14k net
That is real good for the Polish market. It will enable you to save up a substantial amount of money.
That is, again, assuming you are a single male. If you're bringing a wife along, it's still pretty good. Kids that have to be put in private English-speaking schools will cost a lot, though. That is one thing that is quite expensive in Poland.
Also, you mentioned wages and cost of living, but neither of these is important in itself when determining whether a job in another country is worth it. The only number that matters is how much you can put into your savings account at the end of the month.
Someone who can get about 20,000 PLN a month in Poland should have little difficulty getting twice or more that in a richer country. Even with the higher cost of living there, it might well turn out that your savings potential is greater, even substantially so. So make your decision based on savings potential, not wages or cost of living.