What you need is sleep on the plane! Dromoland from Shannon fine Dromoland from DUB 2 1/2 hours down the M7 and then the N18 ending through Newmarket on Fergus.
Auto is expensive compared to stick GPS is a non essential. Make sure All quotes are All inclusive compare Apples to Apples and book direct. US licence holders are hammered on insurance as high risk so that's the bit to watch. Dooley are a decent option but provided you book direct should have no surprises.

You are meeting Irish friends .. Take the Bus or Train to Limerick and have them pick you up there. next day rent from Limerick or Shannon before aiming south.

As Tony states, an automatic car will be much more expensive than a manual one, but the peace of mind may be worth it, especially if you have never driven on the left. Although my husband drove a manual transmission car for 3 years (on the left) when we lived in Australia, he was glad to drive an automatic on both of our trips to Ireland. With all the driving we did on narrow (and sometimes curvy) roads, he said that driving the automatic was just one less thing he had to think about.

I also agree with Tony that a GPS is "non-essential". All you really need is a decent map and a willingness to ask for directions. (Everybody gets turned around in Ireland, even with GPS.) We used the Rough Guide Map of Ireland for both of our driving trips, but I think the OSI series is the most recommended maps.

We rented cars from Hertz for both of our Ireland trips and were completely satisfied with them. You will want to research the various kinds of insurance--CDW, Super CDW, etc. With the exception of the World Mastercard, you will not have insurance coverage with your credit card as you do in the U.S.

Be prepared for sticker shock--automatic transmission car rental + insurance is not going to be cheap. If you think you need GPS, that's only going to add more to the cost.

Be VERY careful. You will be driving on very little sleep on the "wrong" side of the road. IMO this is not a good idea. The bus to Limerick is a much more sensible plan.

Thanks for the advice. I'll think about your responses, especially the sleep advice.

Remember the mantra "Short left, wide right" or you will end up in the wrong lane.

I'd recommend the bus from Dublin to Limerick also. Buses in Ireland are very comfortable and you will be able to enjoy the scenery. GPS in Ireland is a waste of money, as they are not kept up to date. I rented an automatic from Hertz last year, and while it was expensive,I was very happy with it. Be sure to note any defects like bald tires, missing side mirror, dings or scrapes and have them documented, etc before driving off. (Obviously, you are not going to accept a vehicle with bald tires, or missing mirror, but you know what I mean). Happy motoring.

Dan Dooley did the job for us with an automatic and a drive and stay package.. most satisfied!!! A GPS is a huge waste of $$ IMO. If you get lost so much the better to see Ireland. All roads lead to somewhere and if in doubt ask or turn around..

The cheapest rate I've found was actually through Kemwel:

http://www.kemwel.com/car.cfm

It was $100 cheaper than all the other companies I've searched. But obviously you can shop around. I'd also suggest taking a picture of the car from all angles when you pick it up, and again when you return it, so you can dispute any mysterious charges that might appear.

"The cheapest rate I've found was actually through Kemwel"
"It was $100 cheaper than all the other companies I've searched."

Be Warned the forums are full of complaints and bitching from Ordinary people who though they were getting a great deal,, Until they got to the collection desk at the airport! Car hire is pret

Continue...Car hire is pretty much the same from everyone so something a lot cheaper will probably be missing one of the optional (necessary)extras