for that price I imagine within easy walking distance the best hotels would be on Harcourt Street, The Harcourt Hotel, Russell Court and Jackson Court Hotel, you'd probably want to get a room at the back as the street is hopping most nights till about 4.
Have stayed in the Harcourt Hotel and the room was well under €100 for a weekday, hotels.com would be a good place to start.
Have a great break.
Not a hotel.........but I always recommend visitors to Kilronan House - its a really lovely guest house on Adelaide Road - a bit noisy on weekday mornings /early evenings because of traffic but very quiet on Friday/Saturday/Sunday nights. They have a website.