I decided to go with the shoppergroupprice-plugin that is provided by Metapps!
I got it working on a test-site but having problems with it on a site under construction that has been migrated from VM1 to VM2. There I cannot get this plugin working even after doing all the same way as in the other test-site.
I have installed and enabled shoppergroupprice-plugin.
I have installed the product.php file as instructed.
I have made a new shoppergroup "Wholesale" group
I have added 13% VAT tax to the product.
I tried saving a new shoppergroup-price for product shoppergroup Wholesale price-field. When clicking save the price added does not get saved, but the default-price from cost-price-field shows in the Wholesale-shoppergroup-price-field.
Here you see an image of what I mean:

Mettaps, what am I doing wrong? Is is possible the migration process of shoppergroups is messing up the possibility to use the plugin? I did create a new shoppergroup also (ID 15).
Could you have a look and let me know what is wrong?
Thanks!
Anne