You can book these cheap flights to various cities in Australia (Perth, Melbourne, Sydney, Brisbane) mainly within April and May 2015. You may also consider to visit Tasmania for very attractive fare considering the destination. One Way tickets between Dublin and Germany or London should be matter of less than €25 if you book in advance as they are well connected with Ryanair.
Check out your options rough Skyscanner giving you quickly an ideal what your possibilities are..
Booking samples
DE - Dublin - Melbourne - Germany (Frankfurt/Munich) for €664
DE - Dublin - Melbourne and Sydney - Germany (Frankfurt/Munich) for €668
EN - Dublin - Melbourne and Sydney - Germany for €682
EN - Dublin - Australia - London from Ł533
EN - Dublin - Australia - London from €699
Tasmania
DE - Dublin - Hobart/Launceston - Germany (Frankfurt/Munich) for €722
EN - Dublin - Hobart/Launceston - Germany (Frankfurt/Munich) for €746
EN - Dublin - Hobart/Launceston - London for Ł579
EN - Dublin - Hobart/Launceston - London for €763
Booking sample of cheap open jaw flights to Australia from Europe for €664 here. In this case you would be departing from Dublin to Melbourne on 5th of May. Your return flights from Australia back to Germany (Frankfurt) would take place on 26th of May 2015.