PMP Practice: Anticipate future budget challenges

Ember Johansson-Wright is managing a predictive project to deploy a new inventory management system for Velvet Hippo Logistics across fifteen regional warehouses. During budget estimation, the sponsor asks why the budget is 18% higher than a similar project completed two years ago. Ember explains that the earlier project experienced significant cost overruns due to underestimated hardware procurement and installation labor, lessons that were documented in the lessons learned repository. The sponsor is skeptical and suggests using the old project's original budget as a baseline. Ember has access to the previous project's final cost reports, lessons learned register, and vendor quotes from the current market. The project charter has been approved but the detailed budget has not yet been finalized. What approach would be MOST effective for Ember to justify the current budget estimate?