Currently the cheapest way to get SkyBus tickets, that I can find. You can also get a further 10% off on your first purchase from Pelago (~$6 cap, so purchase 2x return for best saving), or get 10% off in the app (probably also single use).
NRMA does have them for slightly cheaper but unfortunately they are "temporarily unavailable". Agoda is also another option but is currently $37.08 return,
You'll also earn 3 KF miles per dollar.
Note that tickets expire 3 months from date of purchase. Activity date does not matter.
And yes, I know there are cheaper ways to get to the airport. But sometimes SkyBus is simply the most convenient option for travellers.
See also: Free DFO airport transfer, for those who have the time and schedule aligns.