Hi,
Greatly depends on the service you want & the agent, as a guide I pay 10% + vat per per year for a "full management service" for property in Celbridge, & I pay 6.9% + vat for a "finding a tenant & acting as a middle person" for property in Tallaght.
If you are new to this I would advise you to go for a full management service or at least get the agent to deal with any queries for you, ie dont ever give the tentant your phone number.
Also need to bear in mind what happens if tenant wants to stay another year at the end of the rental contract, in this case you generally negotiate the agents fee's as the agent does not have to find a new tenant. I have dealt with agents that charge from €150 - €250 per year for addittional years with the same tenant.
Good luck.