I used Arguscarhire.com when i went away in the summer (admittedly not Ireland). They were the cheapest i found. They were effectively a broker for a local firm but were spot on and didn't try to rip me off at all.
Yeah I googled cheap car hire and found them to be quite reasonable. Like a moneysupermarket type search.
Booked it through Hertz via AerLingus with some discount code. Managed to get the one up from the mini economy for 270 Euro in the end.