This is usually the first thing people want to know, and fairly so. The problem is that most price guides either stay vague or ignore the part that really changes the figure: the condition of the room and the amount of preparation involved.
For a standard room in Dublin, a realistic starting point usually sits in the mid-hundreds, with many smaller bedroom jobs landing somewhere around €250 to €450, while larger bedrooms or rooms needing more preparation can move into the €400 to €650+ range. Broader Irish guides can stretch higher again, sometimes towards €800 per room, particularly where preparation, premium finishes or more involved woodwork are part of the job. 
The same principle applies even more to hallways, stairs and landings. Those areas usually involve more cutting-in, more awkward access, more visible woodwork and tighter working conditions, so they often cost noticeably more than a simple square room. Guides for Dublin interiors commonly place these more involved spaces above standard room pricing once detailing and preparation are factored in. 
In the end, the better question is not only “how much does it cost to paint a room in Dublin?” but “what exactly is included in that price?” That is usually where the real difference lies: preparation, materials, woodwork, clean-up and the standard expected once the job is complete.