Fares for the core Dublin Area
http://www.railusers.ie/passenger_info/fares_matrix.php
Exact change helps, note ticket machines will not accept 50 euro notes if the change to be given is more than 18 euro. They do accept credit/debit cards for transactions of at least 1 euro
Book online, 90 minutes before departure on intercity routes. You can collect your ticket at any Irish Rail station with a ticket vending machine (It doesn't have to be the one you choose when making the booking)
Booking offices can sell tickets for use tomorrow
All trains on all routes are now accessible, phone ahead to the station if you need assistance. Not all stations are accessible (Salthill southbound is the only DART platform without wheelchair access)