If you plan to be self-catering then you will need to be somewhere where you can stagger home from the nearest music bar. At that of year you will find plenty of entertainment in Doolin or Dingle, I certainly would second the choice of the West coast from West Cork (nice modern cottages in Schull) northwards to Donegal
Yes, Ireland is not the cheapest place to drink or eat out and I would definately avoid tourist traps like Killarney where prices are raised for the tourist season (actually, forget the prices, just avoid it like the plague anyway) However, I think you will find Irish people friendly and generous. I have been in bars with children where the landlord has insisted on selling us a large 2litre bottle of lemonade or coke at shop price rather than charging us for several expensive mixer bottles.
I'm sure wherever you end up you will have a great time, once you have decided on eventual destination I'm certain you will have no shortage of more specific suggestions