Balance accommodation costs against the cost of taking the bus every day.
Dublin buses cost €2.35 per passenger per trip for casual tourists.
That's Euros, not dollars.
If you're not staying near the downtown sites in Dublin, you will probably make two round trips per person per day by bus: out once to see the sites during the day, and back out again in the evening.
That means a couple can pay €18.80 more per night for a hotel that's close enough to avoid using the buses. If you are traveling with two children, you can afford €37.60 more per night for closer hotels that permit you to avoid using the buses.
And that doesn't include the time savings.
Note 1: Even if you stay downtown, you will still take a bus to Kilmainham Gaol.
Note 2: If you're driving, obviously there is no bus fare, but the cost of parking is astronomical, and the aggravation is substantial.