Fares do change with demand and by date
See
http://www.railusers.ie/passenger_in...ne_tickets.php
New website
http://new.irishrail.ie shows the fares upfront now
Dublin Sligo doesn't have the full yield managed fares just yet, this is in part due to the fact not all stations on the route have ticket collection facilities and indeed the Sligo line is actually quite busy!
Fares online single 10-23 euro
Cash 32-44
Online the system will issue the cheapest ticket depending on the day of the week, so two 23 singles will be 32 in total if Mon-Thurs+Sat
There will be a completely revised structure in 2012 which will really change things