If you travel regularly by train, you can save by buying weekender tickets. Weekender tickets are valid for travel on a Friday or Saturday, with return up to the following Tuesday. The ticket itself says Student / Weekender, but they're valid for anyone.
To buy these, you need a weekender ID card, which you can get at the ticket desk if you bring a passport size photo and 7 euro with you. The ID card is valid for 12 months.
As an example, Ballina 42 euro return, weekender return is 33 euro.