If it's a heating pipe, the system will have to be drained down, leak fixed (which will take 10mins max) and the system refilled. The draining and refilling will take much longer than actually fixing the leak. Could take up to two hours max. Don't know how much plumbers charge in Dublin. Ring one and find out what the hourly rate is. When you do find out I'd love to know too!
If the plumber does his job right he should add inhibtor to system when he refills, cost €20 max.