Although some countries like Ireland don't have very high costs of living like London or Paris.
You should be careful about giving people that kind of information. Also remember that Ireland is a country, not a city! The comparison is between Dublin, London and Paris. In fact in one survey from 2016 carried out by The Economist, Dublin comes in just one place behind Paris in the rankings and another from this year, just one place behind London. Other parts of Ireland are somewhat cheaper to live in but then salaries will be a bit lower too and you will definitely have to run a car if you live anywhere outside the very centre of provincial towns. Dublin pretty much always comes in the top ten most expensive cities in Europe.
Here's a couple of examples of comparisons between Dublin and London, as you can see they are very close:
Grocerie prices are actually 8.66% lower in London!
Restaurant prices only 2.82% higher in London.
Rent - very important - just over 30% higher in London. However much as I love Ireland, you simply can't compare Dublin with London in terms of the amenities and the opportunities available professionally. I would be happy to pay the higher rent to access those.
Now compare Dublin and Paris:
Groceries are almost the only thing more expensive in Paris, 21.56% higher.
Restaurants 3.94% lower than Dublin.
And rent, a fairly significant 15.5% lower than Dublin.
Now to finish, let's compare Dublin and Warsaw:
Groceries 48% lower than Dublin.
Restaurants 57% lower than Dublin.
Rent in Warsaw is more than 60% cheaper than Dublin.
Even allowing for the difference in salaries there would appear to be more of a margin for the OP to save something in Poland.