Knowing ireland

I would recommend renting a car on weekends and simply driving to where you want to go.  It only takes 2.5 hours to drive across the whole country east-to-west (i.e. Dublin to Galway.)

Visit the Burren, Killarney National Park, the Ring of Kerry, Kinsale, etc... on the weekends you have free.  The factory tour in Waterford is fun.  You could do a day-trip to Waterford if your are based in Dublin.  The house and grounds at Powerscourt are not to be missed either, and they are relatively close to Dublin.

When you drive yourself, you can keep your own schedule and stop wherever you want.  I think one of the best lunches we had was a car picnic in the parking lot at the Cliffs of Moher!  Never underestimate your own ability to get along and get around.  You don't need a tour, you need a good map (maybe a GPS) and a sense of adventure!