Well a very quick search using ITA and checking on some websites yields the cheapest options buying from QF or BA. This is a QF flight from Frankfurt (FRA) to Singapore (SIN), then a connecting QF flight from Singapore (SIN) to Perth (PER).
Cost is EUR 871 per person (at current exchange rate, about AUD 1220), so about AUD 2500 all up for both of you, give or take. Dates around Sep 30 are OK. Not a completely horrid price, either. Although this is not the cheapest option, at least you can book it all in one hit and one ticket, which equates to much peace of mind (at least, in the eyes of many who have frequented the forums of late).
An alternative, if you are so inclined, is to consider Air Asia X (D7). They fly London-Stanstead (STN) to Kuala Lumpur (KUL), then a connecting Air Asia flight from Kuala Lumpur (KUL) to Perth (PER). A quick online search gives a cost of
two adults travelling one-way STN-KUL-PER on Sep 30 costs GBP 940 all-up (includes taxes), or about AUD 1500. Now to that figure you would need to add (for both flights) costs of checked luggage, meals and amenities bought on board, and the cost of a flight to get from Germany to London Stanstead for two people. But it's still no where near AUD 2500, however this is
budget travel - you need to adjust your expectations accordingly.
Keeping on the Air Asia and budget theme, you can do even cheaper if you can get yourself from Germany to Paris-Orly Airport (ORY). Two adults on Sep 30 flying ORY to KUL one-way is EUR 612 (or AUD 860) all-in, adding on a KUL-PER sector the next day, which is MYR (Malay Ringgit) 971, or AUD 320 all-in. Add that up and total cost is just about AUD 1200
for both of you, all-in
but you must add checked baggage, meals, amenities and connecting flights from Germany.
Yet another alternative is airberlin. They run some services from cities in Germany (notably Berlin) to Asia, but mainly through codeshare agreements. Their one-way fare is not too bad, e.g. Sep 30, 2 adults, Berlin to Singapore on a codeshare operated by Finnair (Berlin-Helsinki-Singapore) going for EUR 1200 for 2 adults, or AUD 1700. You can tack on a cheap fare to PER from SIN onto that, and perhaps come out cheaper than you would booking with QF or BA.
That should get you started....
