If your local GAA club or soccer club is getting an all weather pitch - approach the builder and ask them for the topsoil that they have to remove for the pitch! Cost - possibly free
Some one told me that you can ask your local county council for top soil and they will deliver it by the tonne.
I can't confirm this as I haven't tried it.
Another option is Landscape Depot in Tallaght. Tel 451 2608. They charged €80 for the first ton and €30 for each subsequent ton. For another €10 a ton they'll bag the topsoil so that you don't have a big loose heap of earth sitting in your driveway.