The idea of buying a car in Ireland makes sense, but not if you look closely at the detail. The main reason why is because cars are generally more expensive in Ireland with second-hand prices generally 20-30% higher than in the UK. Also, while Irish cars are right-hand-drive they use kilometres-per-hour speedometers which would make driving in the UK confusing. It would be much cheaper and more convenient to buy a car here in the UK and take it to Ireland with you, even factoring in the cost of an additional ferry crossing to get there.