Bus hire recommendation

Note that August is peak tourist season.

Do you mean you want to hire a bus so that only your group can use it?

There are dozens of reputable firms: http://www.goldenpages.ie/coach-hire-companies/ It would make sense to shop around and especially compare Dublin / Wicklow-based operators with Kerry ones, as an operator might have a coach in the 'wrong' (right for you) location and you might be able to give you a good deal.

Size (10-60 seats), quality, air conditioning, facilities (toilets, drinks, etc.) and guides (if required) vary hugely, so decide what you want. You need to decide if you want the coach only for coming / going or if you want it the whole time you are there.

As it is a 4-5 hour trip, an alternative might be to get to Heuston Station (Route 46a direct from Dun Laoghaire Station to Heuston) and get a train to Killarney and then use a coach. Note that most Dublin-Tralee trains require a cross-platform change at Mallow. Timetable: http://www.irishrail.ie/media/05_dublincork-tralee_25052015.pdf At least you can get up and walk about on the train, get a bite to eat on the move, etc. Depending on group size, a substantial discount may be available.

Another option might be to fly to Farranfore (Kerry Airport, flights from Dublin, London Stansted, London Luton, Frankfurt Hahn). You can currently fly for under €50 one-way from Dublin. Aircoach operate a Dun Laoghaire-Dublin Airport coach service. http://www.aircoach.ie/timetables

Route 700: Dublin Airport to Leopardstown/Sandyford
Route 702: Dublin Airport to Greystones/Bray
Route 703: Dublin Airport to Killiney/Dalkey