Avoiding fee for pin based transactions

Install Google Pay on the phone and add your cards to it. You can then tap the phone on a POS machine and avoid entering the PIN. You'll need to switch on 'NFC and contactless payments', it's just below Wi-Fi and Bluetooth in Settings/Connections. To answer your question, I'm sure there is some limit but it's greater then €50.

At a given point in time, one of your cards will be the default and will be used if you simply tap the phone against the POS machine. If your keyboard is locked, you will need to unlock it just before you tap. To use a different card in a one-off transaction, (e.g. to use your credit card to buy fuel), open Google Pay, scroll the cards until the required card is on the display and then tap the phone. It will use that card and then revert back to the default. To permanently change the default card, scroll to the desired card, tap the card image and tap on 'make default for contactless'.

You said you're with AIB, their cards will work but for anyone with an EBS card, none of their cards are supported by Google Pay.

Just need to add that they can use Google Pay to tap for payments over 50e as Google Pay contactless works for higher than 50e bills and yes, that's free comparing to using a bank card as a chip & pin.