You are simply not going to find rooms in Dublin for 120 euros/night even when there isn't a special event ... you either have to set your standards lower (much lower), or double the budget. I like staying at the Westin which has a great location and an interesting building (converted bank, and the interior floors don't always line up with the exterior windows) but that usually runs over USD 300 (so a good use of points). Staying by the airport is simply not viable for a lot of reasons; go elsewhere.