Specific discount price per product

Hi,

I've been searching issues and google for hours without finding the solution on my problem:

I'm going to have around 40 vine products in the shop I'm building. Each product have a price if you purchase less than 12 items, and a price if you purchase more than 12 items — it doesn't matter if it are items with different SKU's. The discount prices (the price if you buy more than 12 items) is not a general percentage or a fixed amount off the normal price. There's simply no system for how the discount prices are calculated. I need to type a specific discount price for each product when adding/editing the product (like a new discount price CCK field).

Here are some examples:
vine1 — [ Normal price: 85,- ] — [ With the purchase of 12 or more: 80,- ]
vine2 — [ Normal price: 70,- ] — [ With the purchase of 12 or more: 65,- ]
vine3 — [ Normal price: 75,- ] — [ With the purchase of 12 or more: 69,- ]
vine4 — [ Normal price: 139,- ] — [ With the purchase of 12 or more: 129,- ]

Hope someone is able to help me to solve this.

Thanks a lot!!