PMP Practice: Assess priorities for all parties in the negotiation

Sky Okonkwo is managing a hybrid project at Photon Drift Inc to develop a customer analytics platform. The project uses two-week sprints for the software components and a predictive approach for hardware integration. The vendor providing cloud infrastructure has proposed a contract amendment requiring a 15% cost increase and a two-month extension to delivery timelines due to supply chain constraints. The sponsor, Kenji Matsuda, has made it clear that budget overruns are unacceptable given current market pressures. Meanwhile, the technical lead insists the vendor's infrastructure is critical and cannot be substituted without significant rework. Sky has confirmed that the vendor's competitors could provide similar services within the original budget and timeline, though onboarding would require three weeks. What should Sky do to negotiate effectively?