Taxi fares in Waterford seem to have gone up considerably since the de-regulation milarky e.g. a cab from the suburbs to Waterford City is neigh on €10. Around €30 should cover it to Dunmoer (10 miles), but may be a little more.
Once local cab company is '3 7's and a 10' 051-877710 (no conenction - use them when I'm down there). They should give you an idea.