Many people don’t know that Zen Cart Per User Group Specials also allows you to create per user or group Sales! (In Zen Cart, Sales are per *category* discounts, whereas Specials are per item discounts.)
Creating a per user or group sale looks just like creating a regular sale, except there are settings that allow you to configure it on a per user or group basis.
Once the sale is created, it looks like any other sale when seen by the targeted user or group.