Hello Reinhard,
In this particular case I would recommend you to add 4 custom fields to product -> every field for a different role. Then you can simply use the macros to display the right price based on the role of current user, in the same way modify the transformations, etc. depends where and how exactly are you displaying the price.
Then, I suppose, you will also need to customize the wau how the price is calculated. We have a similar sample how to customize the price based on the currency, so you can take an inspiration from this sample and create the one according to your needs.
This sample file with customSKUInfoProvider could be found in the following location:
Program Files (x86)\Kentico\8.0\CodeSamples\App_Code Samples\E-commerce samples
Best regards, Martin