Here some more info on the business background of this problem.
The surcharge represents the usual overhead costs.
The customer does not want the surcharge to be part of a purchase items' cost price, because then:
- the inventory value of all purchase items would be higher than before
- the costs of goods sold (COGS) of these items would be higher than before.
The latter is important when purchase items are directly sold and not built-in in manufactured items. For such trading goods the material surcharge would be too high, since the overhead costs of trading good sales are lower than for the more complex manufactured parts.
I hope this helps !