Just booked two tickets for my mum and dad for July/August this year

all Y

YYZ-LHR on AC
LHR-SIN on SQ
return same route, same carrier
the SQ on the SIN-LHR is SQ322 which is a 388

$390.25 + $31.50 AE fee X 2

I was pleasantly surprised. I thought the taxes would be around $500