According to the Halide II App Store landing page[1], a one time purchase is $50. Whether or not it's easily accessible in the app is another story.
> In-App Purchases
1. Yearly $11.99
2. Monthly $2.99
3. One Time Purchase $49.99
[1] https://apps.apple.com/us/app/halide-mark-ii-pro-camera/id88...