UK, Ireland /
Moving from Ireland to Poland [39]
All I can say is, it ain't all it's cut up to be. I did the same thing, and after the honeymoon period is over, you will begin to face reality and understand why lots leave. When you first move there it will feel like you are still on holiday, but once settled down, you will begin to experience the reality.
Firstly, good luck finding work, especially one which pays you as well as you get in Ireland. Here, the most important thing is to Learn Polish!!!!. Don't rely on your wife to do everything for you. Learning the language, and speaking it with your wife is extremely important. Especially if you value your own independence.
You will be shocked at how hard some things are compared to Ireland. Bureaucracy is often a frustrating process especially if you don't speak Polish or don't know somebody who can help you with everything. Also be prepared for a culture shock when you experience customer service here, a smile is a rarity (Unlike in Ireland).
As for the average cost of living, it all depends on where you want to go. I believe you could live comfortably of 3-4000zl a month. If you move out of town, then the costs will be less (But then you have less chance of finding work).
Buying land and a house is cheaper than it is in Ireland, and I would highly recommend you stay in Poland whilst the home is being built (To checkup, etc..). Once done, I would recommend you go back to Ireland to pay of your mortgage. (At least then you will have something to look forward to).
I'm only being frank with you, but unless you have something really good to offer on the Polish job market, you are much better off staying in Ireland. Also, ask yourself, why did your wife leave Poland in the first place?
Sorry if I sound like a killjoy, but I'm only sharing my experience. Others may have a very different experience than I have. Good luck