Hello,

This feature is already available in the plugin.

{CF-CustomFieldName} – inserts the contents of the custom field with the specified name. E.g. If your price is stored in the custom field “PRDPRICE” you will need to use {CF-PRDPRICE} tag.

https://docs.wpwebelite.com/social-auto-poster/social-auto-poster-setup-docs/#facebook_settings

Let me know if you want it in another way.

Thanks