How to get cheap train tickets in Ireland

I want to go from Cork to Dublin on Saturday morning and return later in the same day. I'm trying to book tickets but the cheapest I can get is EUR86. How to I get the tenner each way tickets that are always being advertised?

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You need to book online (it is a bit cheaper online than at a railway station anyway) but the €10 fares are usually just for off peak journeys. 

At www.irishrail.ie I did a search for Saturday 28 August leaving Cork at 06.30 arr. Dublin Heuston at 09.15 and return from Dublin Heuston 19.00 arr.Cork 21.58, price €30. Leaving Cork an hour later at 07.30 but returning as before changed the price to €40, plus a booking fee €1 and a transaction fee €2. So far as I remember, if you book seats for several people in the one booking, you just have one lot of fees to pay. The prices quoted above were the cheapest for a Saturday, for standard seats. Premier seats were dearer. 

There are terms and conditions. You book online and pay with credit or debit card, but need to call to the station at least half an hour early to collect the ticket, bringing the credit or debit card used to make the booking (they reserve the right to provide the ticket only to the named owner of this credit/debit card) but if you haven't got the card with you, you should have a passport or valid driving licence. 
http://www.irishrail.ie/home/terms_and_c...

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I just checked the website and it said 30 euro.. Go to the thing on the main page and type in Cork to Dublin, and click enter. Then choose the two trains you want and down the bottom of the page it says "Check price". Click that and then it gives a list of prices :) Those tickets they advertise for a tenner will always say "terms and conditions apply"... That means they're not REALLY giving you cheap tickets.. Bummer. 

But if you try what i said it should work :) 

Have a good trip! 

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Did you look at buying two one-way tickets instead? That can be a lot cheaper. 

Booking online via www.irishrail.ie is appreciably cheaper than buying them directly from the station, but apparently Iarnród Eiréann have only allocated two carriages per train for online bookings, so you need to book early if you're travelling on the weekend of a big sports event (as I discovered the other weekend).