Hopefully this might be helpful to others, especially Three customers such as myself who are having their plans changed!
Meteor are currently running an in-store only promotion on their PAYG plans. Their simplicity unlimited pay as you go bundle is €20 for life if you port your number in-store before March 31st. The plan includes unlimited calls, texts and 15gb of data (Facebook, Pokemon go, YouTube and several others are free to use and do not count towards this allowance). Normally this is €30 per month.
It isn't mentioned online and I only noticed it by good fortune on the LCD screen when I was passing the store in Wilton yesterday. I had been planning to port to them anyway as the Three/Tesco/lycamobile data signal is awful in the area during the day so this was a welcome, if well hidden, sweetener.
MOD EDIT: NOW ON EIR WEBSITE https://www.eir.ie/mobile/prepay/