Translation:We are paying for our food.
I suggest looking here. However, I've also heard Íoc as to mean "pay for", in the sense of consequences (You'll pay for that), where as you use ar otherwise. breis.focloir.ie shows both as possibilities.
So it would be 'taimid íoc ar ár mbia'?
Tá muid ag íoc ar ár mbia, yes.