flightasia: Funnily enough, SQ has its crew who do SIN-PER and SIN-TPE have 24hour night stops. QF's crew regularly do SIN-PER turnarounds, as do Jetstar for SIN-PER and SIN-TPE.
For some flights which only operate 3 times, a week, SQ's SIN-TPE crew have 2 nights in TPE, for a flight time of 4:20.
SQ used to have their crew do tunarounds for PER, but many crew turned up "sick" for those flghts because they were nearly 12-13 hours from time of reporting to work to time of leaving the arrival hall in SIN.
Maybe because of the high AUD, Singapore salaries and those of just about everywhere in the world would be lower than Australia at the moment. However, Singapore has the highest salaries in Asia outside Japan (if even), so it's not exactly a low-cost labour market, and is certainly far, far more expensive than any country in South East Asia.
You also said "My personal view is if an airline wants to hire foreign crew then they should have a AOC in that country and register their aircraft in that country."
Jetstar Asia has a Singapore AOC and registers their aircraft in Singapore with a 9V code. Jetstar Asia operates 3K flights SIN-AKL with SIN-based crew using the SIN AOC.