I'm looking for a solution to a very tricky price rule: The client gives 20% discount to every discountable article (if an article is discountable is set in an article attribute) only for a special customer group. This far it's easy to set up in Magento, but here we go: When the discounted subtotal gets higher than 400, a tier discount comes to life: 40% on articles X, 33% on articles Y, 25% on articles Z and 20% on all left discountable articles. The big problem I've got here, is that the tier discount isn't based on the first 20% account, it's based on the original price again.
And I can't figure out any way to do this natively in Magento. Unfortunately catalog price rules and cart price rules are completely independent, so this is also no option.
I'm not afraid to do some extra coding, but I have no idea where to start without messing up the complete Magento installation.
In my opinion there are only 2 and a half ways to get this done but I have no idea how to achieve this: 1. Hard code the rule. 2. Adding a custom condition to the rules editor or nesting the first 20% rule.
At the moment, I'm completely lost on this topic, so please, every Magento expert out there, I'm grateful for every hint, tip or advice.