The Jetstar Singapore cabin crew base can be thought of as "casual" rather than full time. The base pay is about S$1,200 then they only get paid as they fly. It is misleading to say that they are paid a slave wave because I know Jetstar cabin crew myself and they get about S$4k a month after flying.
You could then say that the Jetstar Australia cabin crew on casual terms are paid $0 - since their fixed pay is zero.
SQ does not underpay their cabin crew, even by Western standards, which is why they get the quality of cabin crew that they do. Since every SIN-based asipiring flight attendant would always use SQ as their benchmark, if Jetstar really underpays their crew to such a horrid extent, then who would want to join them?
SQ cabin crew also have low fixed pay and a very high variable component each time they fly - so you can think of them as "casual" as well. I think the base is S$1400 to S$1800 a month for entry level cabin crew, but each time they fly they get loaded with allowances. I know the SIN-FRA-JFK turn (7 nights) is well in excess of S$2k in allowances. In a good month, some can make S$7,000.
Generally, white collar wages in Singapore are among the highest in Asia and comparable to Australia and other Western countries. Due to the low tax though, companies can pay a lower salary and ensure you still end up no worse off or better off than if you were paid the equivalent sum in a typical Western nation. This is the same for the Middle East.
It's just that the AUD has moved 20% above its long term average, which I guess also impacts the cost of doing business in Australia. Through the 1990s, AUD:SGD was around parity. In the past 8 years it has moved to around 1.20 though in the height of the financial crisis in 2008-2009 it went below 1.
If you earn S$200k, which is A$165k, you will end up with an after tax salary of A$143k. If you earn A$200k, you will end up with an after tax salary of about A130k. I think the tipping point is around A$60k - Assuming current exchange rates, if you earn $X in Singapore dollars in Singapore, you would still end up ahead compared to if you earn $X in Australian dollars in Australia, despite the exchange rate differential.
I do empathise with Jetstar Australia pilots who feel their jobs are under threat. Not too long ago, the SIA unions forced the company to shut down all the expat flying bases. SIA used to have pilot bases in London, Perth, Sydney among others, and they have all been shut down. It's been ages since I've been on an SIA flight with an expat Captain, and I fly them about once to twice a month.