Price List question in CRM 2011

In CRM 2011 online, how can we restrict access to Products and Price List per Business Unit. 

i.e. Say Product A is part of Price List A; Product B is part of Price List B; 

I have Business Unit A & B. 

Users from Business Unit A should read Price List A and not Price List B; 

like wise, Business Unit B users should only see Price List B and not Price List A. 

Since Products and Price-lists are organization level entities, how can we achieve this through security roles or something. 

Any thoughts will be appreciated.