Material Request to Purchase Order using Selling Price instead of Buying price


Hope the title is clear, eg:

-> I create a Sale Order with 1 item :
- Item buying price : 10
- Item selling price : 20
-> Sale Order is used to make a Material Request
-> Material Request is used to make a Purchase Order
- Price of item in Purchase Order is 20 (and should be 10, right?)

Any idea?