Octavo costs US$ 24.99, or your country’s equivalent. It is solely sold through the Mac App Store. This is a one-off payment, not a subscription.
Before purchasing Octavo, you can try out all of the features without restriction, but a banner is placed over the bottom of every printed page. This lets you see if Octavo’s features can meet your needs, and when you’re ready you can unlock Octavo via in-app purchase.
Additionally, Octavo’s two mini-zine templates are completely free to use. They don’t have banners on, and there is no obligation to pay to unlock Octavo if you’re making mini zines.
You can purchase from within the app, by clicking the orange “Unlock Octavo” button at the top corner of the document window, or by going to Octavo -> Settings… and choosing the Licensing tab.
If you have previously purchased Octavo, but Octavo is not showing as unlocked, go to Octavo -> Settings… and choose the Licensing tab. There you will find a button to Restore Purchases.
Your Mac must be logged in to the same App Store account as you purchased Octavo from.