Most visitors to Ireland either bring their own car by ferry from Britain, or they fly and hire a car.
If you are hiring a car, you need to know that an automatic will cost half as much again as the identical manual gear box model.
Petrol is currently about 1.20 euro a litre, thats about 80 pence sterling and about $1.50 a litre in USD. Thats about $6 a US gallon. Diesel is a small bit cheaper. Most hire cars will give you 40 miles to the gallon or more.
Visitors are often surprised by how big Ireland is. It will take you seven hours to drive from one end to the other. The Island of Ireland is actually two countries, Ireland and Northern Ireland. Northern Ireland is part of Britain. From Dublin to Belfast will take you a good two hours motorway driving. Dublin to Cork will take you between four and six hours depending on the time of day.
The only motorways in Ireland are around Dublin. The motorway speed limit is 120 Km/Hr (75mph) The speed limit on National roads, N7, N8, N25, etc is 100Km/Hr (62mph). On Local roads the limit is 80 Km/Hr (50mph). National roads go through all sorts of towns and villages where you will find shoppers double parked, so...