same as anywhere, it depends on size of plot, where in the country it is, if planning permission is already granted, if teh site is serviced by electricity, water etc...
He should decide what he needs and narrow it down. A half acre in rural leitrim will cost a hell of a lot less than the same size in dublin.
We found Southern Ireland extremely expensive in most respects. Cost of living is high and house prices seemed high too for what you could get. We were self catering and couldn't believe how high the shop prices were and eating out was really expensive. We couldn't afford to retire their. Lovely holiday in County Clare but we came back broke!!