Car Hire is probably not a regular purchase for most people – maybe 2 or 3 times a year for holidays or when the main car is out of action.
Most visitors coming to Ireland arrive at Dublin Airport – so we did a quick comparison of prices for 1 week’s car hire at Dublin Airport in May 2010 . The price we compared was for  a manual Ford Focus 4 Door (or similar)  -  These are the prices we were quoted online from various car hire companies for a 45 year old driver. (Quotes obtained March 18th 2010  for 7 days hire from May 1st to 8th 2010)

The cheapest price that we could find for the seven days car hire at Dublin Airport was from  Thrifty – they quoted us €122 ( 94 plus 28 Airport Collection Fee).

Other prices for Car Hire (lowest price first)

Knock Car Hire €132 (VW Golf)
Avis £169 GBP  (approx €190 euro)
Holiday Autos £173  GBP = approx €194 euro
Auto Europe £183  GBP (approx 205 Euro)
Europcar €214 Euro
Budget €229 Euro plus €28 Airport Fee) = €257
Hertz €336 GBP (about €376 Euro)

Of course these prices may well differ when you try and book – but it is a useful guide to the amount you can save by shopping around.  When we did this quick comparison for Dublin car hire – the difference between the cheapest  at Thrifty and the most expensive car hire was almost €250 Euro for a week .
There are reports of a possible car hire shortage in Irleland in 2010 – especially in the summer months – so if you know of anyone needing car hire in Ireland – advise them to book early .

Booking car hire online before you travel is typically cheaper than just turning up at the airport. Also – you have a much better chance of getting the type of car you want when you book in advance online.