When you complete a tax return (assuming you are Irish resident) you need to show ALL of your income from all sources. Therefore the cost will depend on your overall situation and complexity of your tax return. Would need more details to advise.
Assuming simple return I would normally charge €300 to €400 plus vat assuming co-operation from the client. Not a lot of work involved but in order to justify keeping a file open I would need to charge this much. Extra €150 per additional house thereafter. Dublin accountants would probably charge more.