Please refer to CullAi product page for latest pricing information. At the time of writing this article payment for Standard version is done inside app File Menu -> Purchase using Apple In App Purchase. You can also take Free 14 day Trial of Standard version and then decide to buy Standard version. As payment is done through Apple In App Purchase, your payment details are only exposed to Apple making the transaction safe. As we currently don't have subscription model, Apple charges you only one time when you actually purchase Standard Version after confirming with you.
CullAi is currently heavily discounted as we are going through getting feedback and adding new features cycle. Once it is optimized for all workflows the final pricing will be updated. Our early adopters will get free lifetime updates.