Zen Cart Quantity Discounts (native) on Listing Page
The native Zen Cart quantity discounts block on the product info page looks like this:This block can also be displayed on the product listing page.
I have developed a number of these kinds of modifications over the years, and this page is designed to show you what's possible for your store.
Relevance: Zen Cart™ 1.5.x
Cost: Based on your requirements, starting at $300. This is not a plugin; it's custom software developed for your needs to your specifications. Before I can give you a final estimate, we need to discuss your needs.
Want something similar for your store? Great! Contact me with your requirements.