I mean, that's pretty flexible. At $17.99 (AUD) per month it could fit into the $1 step model, which starts at $0.99, maxing at $139.99
They charge $19.39 for the same subscription if you buy it direct. By the logic of Apple taking a 30% cut thereby pushing up the price of doing business, you'd think they could charge $12.59 to direct customers and take the same profit out.
(This is month by month subscriptions to NordVPN)