If you'd prefer to buy a phone prior to travel, you might have a look at the Motorola V-551, which you can find on both Amazon and E-Bay. I've always found that model to be a robust and reliable phone. Texting takes a bit of practice since it uses "predictive text entry", but it's really not that difficult.
If you buy a phone now, you can use it either with a SIM card purchased in Ireland OR a SIM card from one of the travel phone firms such as Roam Simple, Cellular Abroad, Telestial, Mobal or EuroBuzz (there are others). These firms also offer phone and SIM packages from about $5 for a SIM and $29 for a phone. Many of these use numbers based in the U.K. so the rates are fairly inexpensive and post paid billing so no need to top-up. Check their websites for details.
If you'd prefer to buy a phone when you arrive in Ireland, I'd suggest stopping at a Carphone Warehouse. They appear to have at least three outlets in Dublin. They represent most of the cellular networks so have a wider selection of both phones and calling plans, and the staff will be able to help you choose the best plan for your situation.