How to anchor tiered pricing with a powerful supplier for 12-month cost certainty?

[JustinM]

I'm a project manager in the construction industry, and I'm about to enter a tough negotiation with a key supplier whose material costs have skyrocketed, threatening to blow our budget on a major development. In past negotiations, I've focused on getting the lowest price, but this time I need to preserve the relationship while also securing some cost certainty for the next twelve months. I'm planning to propose a tiered pricing structure based on volume commitments, but I'm unsure how to anchor the conversation effectively. For experienced negotiators, what tactics have you found most successful when dealing with a powerful supplier in a volatile market? How do you prepare your BATNA and when do you reveal it during the discussion?