If you are transferring within the Eurozone, it is very simple: You pay for an international transfer as much as you would for a local Irish one. For many account types, this means zero fees. In other cases, it could be about 20 cents. Either way, if there is a fee, it gets charged on top of the amount you are wiring - so if you transfer €100, the full €100 will get sent but you might be charged €100.20 for it. The recipient pays nothing.
If there is a currency exchange involved, it is impossible to predict precisely how much will get transferred. Rates change daily and there might also be fees/commissions.