Now that Spotify are raising their prices (again), here's one way to drop the $18.99 to $15 for now.
Can get monthly digital gift cards for $15 each. Need to have a Qantas frequent flyer membership. Just select 0 points in the 'Points Plus Pay' section.
Only applies to individual plans, not family/duo etc.
Not the biggest saving in the world, but if you're going to stay signed up anyway and have a Qantas account, easy enough.
Alternatively if on android or windows then just run modded versions for free premium