You already have the direct costs of 8.30 plus the employer's PRSI. Also add indirect costs of office space, office supplies and equipment, provision of PRSA scheme, and other issues some people don't think about prior to employing someone (time taken to train and manage for one).
Bear in mind, it can be difficult to fire someone in Ireland, especially if they actually know the level of legislative protection they have.
Please ensure you provide an employee contract (stating issues such as rates of pay, dismissable offences, probationary period etc etc) as in the absence of one, you don't have much to stand on if you want to rid yourself of the employee and they challenge it You can put anything you want in an employee contract, and will help your case in the event of an unfair dismissal case.
Sorry to dwell on the downside, but I've seen people taken for a ride by poor employees and have suffurred for not being able to do anything except pay them off.
On the other hand, your employee could earn you lots of extra money by helping your business grow.
Depending on the work you want done, you may also have the opportunity to subcontract the work cheaper or at a comparable price than you can employ someone directly to do it