Just a quick note to say I recently stayed at the Avoca House B&B in Dublin - it's located in Drumcondra just ten minutes from the city centre. It was very reasonably priced, spotlessly clean, warm and very comfortable. The owners were very pleasant and friendly as well.
It's a ten minute bus ride to O'Connell Street and a nice neighbourhood. If you are looking for somewhere nice, reasonably priced and convenient to the city centre, I would recommend the Avoca House B&B on Hollybank Road. It is a few minutes walk to the main road and close to Fagan's Pub which apparently is the Prime Minister's "local".