Hi
First of all you should raise MM related issues in MM forum for right answer..However..
1. Standard cost is basically your plan price based on annual / monthly planed expenses defined in KP06 at various cost center level for individual material (Semi fin & Fin) and these materials having price control as "S" in accounting view 1
2. Purchase info records is maintained in ME11 to keep purchase related information in combination of Vendor, Pur org, , plant and Material where you can maintain price, conditions etc to be used for pricing and other purposes.
3. If you want to cost your sales order items you can use standard cost for pricing your SO items
I think I have put some lights on your query