My quote was for SIN - CNS and then CNS - SIN not as per your CNS - SIN - CNS.
Have another look on the days I quoted - this is a direct copy from the web site.
As AO are not flying this route any more the comparison is hardly valid.
However if you were to factor in inflation etc. etc....
I question whether 4PWs example of $900SGD was ever available.
If you wish to fly CNS - BNE - SIN and get a cheaper flight then so be it.
Sometimes time saving comes at a premium.