To set a specific Price List Id for Portal User, first expose the Custom fields in your Users profiles by going to:
Administration > Users > Manage Profile types > Basic profile
Click on the CRMContacatPriceListId and under Appearance tab, select “All screens where you work with user profiles in the Backend”. Then click Done and Save changes.
Administration > Users > Select a User > Enter the Price List Id to be assigned from CRM in the below Field.
In some cases (e.g., if Portal user is anonymous), you may want to set up a default price list. To Set the default Price List for Portal Users, go to:
Administration > Settings > Advanced > PortalConnectorMvcEcommerce