Custom Apex REST services are the optimal solution for integrating Salesforce with an external PIM system.
When a product is created or updated in the PIM, the external system can make a REST call to a custom Apex REST endpoint in Salesforce, which then can create or update the Product2 and PricebookEntry records. This method allows using custom settings to determine the Pricebook2 dynamically.References: Apex Developer Guide - Exposing Apex Classes as REST Web Services