Need a more specific price calculation rule in Drupal Commerce
Depending on your multiplication factor (I suppose you want to give a discount), you might want to try Commerce discount which has support for discounts per order and discounts per product. 


  Commerce Discount provides a new user interface for defining and
  managing product and order level discounts. Using just the core
  pricing system of Drupal Commerce requires knowledge of how to use the
  Rules UI, which is beyond the capabilities of most merchants.
  Additionally, the core system cannot support order level discounts or
  certain types of shipping / product discounts. This module addresses
  all of those things.


The role based discount condition is provided by Commerce discount extra.