Yes, rentals in Dublin can be very cheap, but pay attention to the terms and conditions of the rental (Costco or Priceline--they are likely both the same), specifically around mandatory insurance. It's common in Ireland for then to lure you in with a low rate and then spring the insurance on you at the rental counter. If you have a credit card that provides you with CDW in Ireland, be sure to bring a letter of coverage which is obtainable by calling the number on the back of your card. Read through the T&Cs carefully, and stick to the major rental brands like Hertz, Avis, National, Enterprise, etc. to lessen the chance of unexpected charges.