Hi
I assume that your RMs are having price control 'V'. You can have 'planned price' option in your valuation variant for material valuation as a last option. In the cases referred above you need to maintain planned price manually in the material masters with effective date. In this way, at the time of std cost calculations system will pick price of material from that field of material master.
Moreover, quantity structure indicator has nothing to do with the problem you are facing. Quantity structure only refers to the BOM and routing associated with your material.
Regards
Rajneesh