It looks like there’s no ready-made solution for your needs right out of the box. One option is to break your quotation into multiple lines, with each line reflecting a different pricing tier.

Alternatively, you could create a custom discount module to handle it more seamlessly. There’s already a similar module available that might be worth exploring: "Tier Pricelist in Sale" (https://apps.odoo.com/apps/modules/18.0/evo_tires_price).  It could be a good starting point if it aligns with what you’re after.