Sorry, but while that concept has been mentioned in past forum topics, the capability to set different sales prices for inventory or non-inventory items by customer does not exist. Nor would its implementation be simple. The difficulty would be the need to create and maintain separate, multi-dimensional price matrices for every customer encompassing all inventory and non-inventory items (because those are treated identically except for quantity-counting functions), all employees and/or pay grades, and possibly quantities. In other words, once you open the door, there is more to the issue than how much you charge for a task.
See, for example, these topics—all returned by searching the forum for “customer billable time” or “pricing levels”:
But there is nothing wrong with billing services via non-inventory items rather than billable time. In fact, there are strong arguments against using Manager as a time clock into which every employee enters their billable hours, unreviewed and unapproved by supervisors. I’ve worked with and for a lot of companies over the years. Never once have I seen a situation in which employees are given direct access to the primary accounting system for timekeeping functions. The risks and complications of errors are just too great.