You can rent a car through a few places. Europcar, budget, sixt and others. They all work out pretty much the same price to be fair. The biggest complaint I have about car rentals is that if you book online (also this is cheaper than booking over the phone) when you get there to collect the car you are also charged a pick up fee, extra insurance is needed and then a few other things thrown in for good luck. You might book a car assuming it to be €70 and it could easily be €140. It is something to be weary of. Also, budget car rental in drumcondra have the worst staff in the world. I have rented there a few times and they will literally give you verbal abuse for no reason, I feel bad for the tourists. I stopped renting cars from there as a result, even if the price was cheaper.