What is an easier approach to implement HR and Shared Services Model, that could bring the change and have its acceptability at the same time?

A recommended approach for wide acceptance of a 'Shared Services Model' is to ensure that the business has an industry recognized Enterprise Resource Planning tool implemented at their business where the entire operations of the business and the benefits or value-add can be measured in a timely, efficient & logical manner in the form of dashboard reports. This type of reporting would also identify all business processes / areas of operations where the organization's resources are being utilized. The Finance operations of the business would then be able to generate effective reporting to determine what percentage of resources are being utilized in which operations/business sections thereby leading to a convincing idea of utilization of Shared Services and effective distribution of such services across entire operations of the business.

If ERP is very expensive to be considered, for the wide acceptance of Shared Services, the business should at the least consider the deployment of consolidated reporting structure which then leads the organization to think in the route of shared services.