This is my saviour. It can be yours as well :) Whenever I'm late for work or especially air port (can't mess around with that one). I drive through this beautiful tunnel. It costs, but it costs €3. It also costs €10 during busy times. It always messed me up when I was trying to remember when it costs €10. It's important to know and remember, because once you are there, there basically no turning back :-( Had made that mistake few times.
Times are quite simple: 06:00 - 10:00 from north side (outside Dublin) is €10, because everyone's rushing to work. 16:00 - 19:00 from south side (Dublin port) is €10, because everyone's going home from work. Other times are €3 plus weekends and bank holidays.
This is the website to check on prices http://www.dublintunnel.ie/tolls_and_permitted_vehicles/.
There're speed cameras, but only occasionally - I was informed - police would be waiting for you at the end of a tunnel. I've been traveling 180 km/h there and not a bother, but never again. Not worth it, as tunnel saves quite a bit of time already on a maximum speed of 80 km/h.
TIP: travel at maximum of 92 km/h speed and cameras won't pick up you. Well, I mean your registration plate number won't show up on electronic notice board. I drive at 92 km/h with cruise control and perfect, have tried 93 km/h and notice came up on the board with speed of ~86 km/h or so. 92 is the magic number, if you want to rush a bit more. read more