Online rail fares V buy at counter: what is the price difference ?

The station fares are available at >> http://railusers.ie/passenger_info/fare_calc_2022.php

In a way they're the maximum fare on a given route. Return fares seem to generally match online and at stations, but single fares are pretty much always 50% that of the return fare online, whereas a station single is hardly any cheaper than a day return. Online fares also don't make a distinction between day and open returns (they stick to the day return fares), so a two-day return trip is again cheaper online than at the counter.

For example, Galway–Dublin Heuston is a €29.30 adult single/€32.00 day return/€41.70 open return from the station, but €15.99 adult single/€31.98 adult return online.

The fares available at the station are also listed on the Irish Rail website, under the rather obvious heading "Fares and Tickets".

Click on the appropriate route.

There are also off-peak promotional fares available on the Drogheda and Portlaoise to Dublin routes only at the station - these are listed in the link above.

Family tickets (up to 2 adults and 4 children) are only available at stations, as are the unlimited travel tourist tickets.