Go go go! Belfast to Melbourne haven't checked a wide range of dates yet but £309.82 with lastminute.com!!!! Scotland airports cheaper from £215 for Perth.
Seems to be March will update thread with dates in a second as the screen shot is just a few days I'm trying other dates! *May, November, December dates found** Also seems to work for EDI and Aberdeen too with variety of Oz airports too. You need to try a variety of dates, read the thread some examples in there!
2 weeks in May for £306 each (screen cap is for family of 4)