Custom day trip from Dublin?

I am on the RS 14-day Ireland tour this fall and will be in Dublin for a few days beforehand. While I am in Ireland, I'd like to go see the village where a relative's great-grandfather came from: Bekan, in County Mayo. It is closest to the Westport stop on the RS tour--50 min drive away--but it looks like we are only in Westport for the evening, so I am looking to take a day trip out of Dublin before the tour. On the way, I will also get to see a part of Ireland where RS doesn't go. Does anyone have a recommendation for a tour company/driver who would take one person on a custom route like this? DayTrip is an option, but it would be nice to have a tour guide who could provide insight into what I would be seeing. Maybe there will be suggestions in the RS guide book, but I have been told we won't get that until June. Thanks!