Hi volkerforster ,
Thanks for your post.
I think you misunderstood what my colleague Andrea said. The complete phrase was: "Cause in order to make imports and exports we recommend to use Export Pro as is 100% compatible with our ATUM features".
ATUM Purchase Price is an ATUM field, so it's an ATUM feature. We create almost all our fields in custom tables for performance reasons. The reason isn't to prevent third-party plugins from accessing the data. Our code is accessible and our custom tables can be queried. Any third-party software developer who wants to access our data is free to do so. What we can't do (I hope you understand) is implement synchronizations to the multiple existing plugins.
A function to use ATUM data with a third-party software other than these ones would probably need custom development. You are free to develop it (or hire a developer to do so) and share the code with the community if you want to. Indeed, ATUM is open source so you can make a pull request to its repository. We'll be happy to include it if we find it useful.
Best Regards,
José Andrés