as to your pricing issue - I saw that on another post - and that is the preferred way - one topic per post thread - makes it easier to search for things, too.
I don't have a satisfactory solution for you, least not yet. Was hoping someone else was doing something similar and would answer. I can't seem to make it work on the out of the box Abantecart. These is an extension called Flexy Promotions that might work, but I have no first hand knowledge of it. Perhaps if you make a post asking that specific question would get you an answer.
Lee