Cost can be argued against lost production, if you have a fault you have lost the whole production area with your design, yes these outlets are costly but to comply to regulation regarding disruption then you have to explain this to the customer, having done commercial and industrial most of my career, I would never fit a 30mA front end on a distribution board unless special circumstances exist and/or it was otherwise requested by a designer of the install if that wasn't you - even then I would be holding a meeting to express my concerns.
The extra's to have RCD protection at the point of load where upfront protection isn't needed for cables etc may be thousands of pounds but to lose half a day or more production while an electrician comes to clear a fault they cannot isolate would probably dwarf the cost of designing it correctly in the first place, if this is about saving a few quid then you need to have a sit down and talk with the customer.
