AU recently had their sub increase which brings them inline with $15 USD. However, NZ and CA pay more than US.
Australia pays $19.99 AUD = $15.19 USD
New Zealand pays $24.99 NZD = $17.80 USD (18.8% more than USD)
Canada pays $21.99 CAD = $17.08 USD (13.9% more than USD)
AUD Price Change (Blizz announcement)
CAD Price Change (Blizz announcement)
US Price Increase Incoming (Player speculation given CAD/NZ pricing)