The Bruce Shaw Partnership website gives useful information.
http://www.bruceshaw.ie/industry_info/irish_contruction_costs/average_construction_cost_1/
1250-1600/sq.m. suggests a rough range of 255,000 to 297,000 for the 2,000 sq.ft. unit.
But that's for estate house level finishes for a 100sq.m. house.
A larger house, a demanding client, costly finishes, state of the art comms and entertainment systems, "American" Fridges, Washing Machines and Dish Washers could easily increase these estimates by 50-100%.
Similar a self-builder could dramatically reduce these costs.
And then there is supposed to have been a drop in prices across the board.
For other cost estimates and the pros and cons associated with builders and self- build, certifcation and insurance, the risks associates with using or not using professionals, you could search this posts on site.
HTH
ONQ.