Check out following tips for cheap accommodation in Dublin:

Celtic Lodge Guesthouse and Bar
Twin Room for 1 or 2 people, Ensuite Facilities, Full Irish Breakfast also included.
From: €39

UCD Village
Single Room, in a Shared Apartment. Apartment consists of four single bedrooms with 2 Bathrooms with Sitting and Dining Area.
From: €40

Travelodge Castleknock
Room has 1 Double bed & 1 Double Couch Bed, to accommodate up to 3 adults or 2 adults and 2 children (children under 16). Rate does not include breakfast.
From: €45

Dublin City Travelodge
Double or Twin Room, ensuite bedrooms. Please Specify in Special Requests Box whether or not you require a Double or Twin. Please Note Breakfast is NOT included. During the weekend there is a minimum stay of 2 nights required.
From: €49

Airportview Hotel
Room has 1 Double bed & 1 Double Couch Bed, to accommodate up to 3 adults or 2 adults and 2 children (children under 16). Rate does not include breakfast.
From: €49

Travelodge Dublin Airport
Room has 1 Double bed & 1 Double Couch Bed, to accommodate up to 3 adults or 2 adults and 2 children (children under 16). Rate does not include breakfast.
From: €49

Marine Hotel
Spacious Double and Single Bedded Room.
From: €50

The Charles Stewart Guesthouse
All rooms are en suite and are fully equipped with television and tea/coffee making facilities. Include full Irish breakfast.
From: €50

The Montrose Hotel
Stay for 4 nights in a Double or Twin Room and save 40%. Breakfast is NOT included with this offer. Please specify in Special Requests Box whether you require a Double or a Twin Room at time of booking. A minimum stay of 4 nights is required with this offer.
From: €52

Hotel Isaacs
Twin or Double Room (please specify in Special Request room type required- subject to availability), private En suite, tea & coffee making facilities, ironing facilities, TV, telephone, hairdryer and in room safe. All taxes included.
From: €56

Plaza Hotel
Double or Twin Room for 1 or 2 people, En suite. Breakfast included.
From: €59