What are cost of customizing MS project for the web?

Question

As we consider enterprise-usage of MS Project for the Web, we might want to make additional customizations. These might include adding additional fields (about 25 additional) to a template, creating customized picklists for select fields or additionally, we may want to enhance dashboards/reporting visualizations beyond the basic out-of-the-box features. What should we estimate in terms of the costs of such enhancements and customizations? Does anyone have a rough estimate about how much time/budget we should allocate for this type of work?