So the cheapest Manchester and Liverpool return is £73.31.
But don't forget Ryanair charges you £5 per return journey to check in and also charges a booking fee, which changes depending what card you use (find out how to avoid the booking fee here).
The return fare on the Terravision bus from Manchester Shudehill to Liverpool Airport is £10.
The train fare from Manchester Piccadilly to Manchester Airport is £6.40 after 10:00 or £7.60 before 10:00.
From the airport to Dublin

The airport is six miles north of the city centre.
From outside the terminal, you can get the Dublin Bus Airlink 747 or 748 service, which runs to the Central Bus Station every 10 minutes or less and costs e6 for a single and e10 for a return. Journey time is 35 minutes. A taxi would cost e28.
Other flights
Another option would be to fly from Manchester to Belfast on bmibaby and then get the two-hour train south to Dublin.
But those flights would cost at least £35, so it would be more expensive and take longer.
Ferry - £55
The ferry goes from Holyhead to either Dublin or Dun Laoghaire. Going to Dun Laoghaire is often cheaper and is 45 minutes away from Dublin by Tube.
There are three ways of reaching the ferry.
Car - £26
You can drive and park for £5 in a car park 500 yards from the ferry (there's even a free bus between the two).
The journey from Manchester costs about £13 in petrol each way and takes roughly two hours and 15 minutes via the M6, M56 and the A55.
Train - £27
Manchester to Holyhead takes 3 hours and 19 minutes changing at Crewe or Chester. The train station is a five-minute walk to the ferry.
You can book for £27 return via National Rail or book a train and ferry package through Stena for £55 return.
The cheapest ferry (not including train) we can find is £33 return from Holyhead to Dun Laoghaire so it makes sense to book the whole thing through Stena.
Coach - £50
The good news is the coach station. The bad news is, it is only served by National Express and returns cost £50 and arrive at ridiculously unsociable hours.

Stena Ferry Times:
Holyhead to Dublin
Aug 3 board by: 09:30 departs: 10:00 arrives: 12:00
Aug 4 board by: 09:30 departs: 10:00 arrives: 12:00
Holyhead to Dun Laoghaire
Aug 3 board by: 13:05 departs: 13:50 arrives: 17:05
Aug 4 board by: 13:05 departs: 13:50 arrives: 17:05
Dublin to Holyhead
Aug 5 board by: 07:35 departs: 08:20 arrives: 11:35
Aug 5 board by: 20:30 departs: 21:15 arrives: 00:30
Dun Laoghaire to Holyhead
Aug 5 board by: 12:45 departs: 13:15 arrives: 15:15

Arriving in Dublin
The town centre is four miles east of the ferry port. A taxi takes about 15 minutes and costs about e12.
The number 53 bus from outside the port will take you to Dublin Bus Station on Amien Street for e1.80 single.
You will have to pay for either in euros, but there's a cash machine outside the port building.
Arriving in Dun Laoghaire
The ferry port is right beside Dun Laoghaire DART (Irish Tube) station. From there, you can get the DART north to Dublin.
It takes about an hour to reach Connolly Train Station in Dublin and services run every 10 minutes or less throughout the day. An adult single costs e2.30 or a three-day pass costs e11.40.
Getting to the stadium
On foot

The Aviva Stadium is two miles south east of Connolly Train Station. and would take about 40 minutes to walk there.
It's slightly quicker to walk from St Stephen's Green, which is a mile away.
Walk up Merrion Row, Baggot Street Lower, Baggot Street Upper and cross the Grand Canal at Baggot Street Bridge.
Then go straight down Pembroke Road and cross the road at the junction of Northumberland Road 0and Merrion Road.
By Tube
Get the Dart from anyone of a number of city centre stations to Lansdowne Road Station, which actually passes under the West Stand. An adult single costs e2.30, a return costs e4.20 or a three-day pass costs e11.40.
By bus
Services 7, 8, 45 and 84 go past the stadium. A single costs e1.80.