I am going to support Undo and tell you to use the ATMs. I was in Szczecin recently, which is a small city compared to Krakow, and there were a lot of ATMs, all from reputable banks, all in well lit and busy areas.
As Poland is considerably cheaper in Ireland, while you may face additional fees for taking out from the ATM on your debit card, this will not be a significant issue as you will be saving on everything else.
In Szczecin, a good steak dinner in a nice restaurant cost roughly €6, a pint of beer €1.20, taxis were cheap, people were very friendly, tourist attractions no more than €2 entrance.