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As mentioned, the free version of the Themify Builder plugin is only capable of creating / editing pages or posts, the paid version allows editing the entire theme.
Additionally, while the core Builder plugin comes with a few standard user interface elements, there is an Addon bundle (not available with the free plan) that extends these to add elements such as pricing tables, WooCommerce products, sliders etc. In total, the Addon Bundle adds another 25 interface elements to the Builder plugin.
There is only one pricing plan for Themify Builder Pro - $69. This is not a subscription, although support will only last for one year, and you will not be able to update the plugin after that point.
So although it is a one time fee, to keep the plugin updated you would need to renew annually. A renewal with a 30% discount.
Additionally, if you wish to use their Addon Bundle, that would set you back another $39.
Themify Builder is a reasonable if somewhat rudimentary option, and can be cost effective if you're an agency, however the requirement for yearly renewals if you want to keep the plugin updated, means that in the long run something like Divi might be more reasonable in that situation.