Singapore is waaaaayyy cheap compared to Tokyo. I'm being honest here, because the amount of money I dropped on my Suica in Tokyo was unbelievable. The transportation in Singapore is decent, just don't expect Japanese standards of course.
OP if you're planning to travel around Japan remember your JR Pass, which is actually pretty pricey.
I'd say put Indonesia/(Singapore?)/Malaysia/Thailand along that same line because it's cheap to get around on budget airlines. Australia seems a bit 'off' in that itinerary but if you're willing to sit it out from Singapore to Australia on a LCC airline, Scoot is really cheap.
p/s: I'm assuming your tickets are not bought yet.