Possibly the most complicated Addon I have ever used it is also one of the most powerful. You can build custom Visual and Audio warnings for virtually any situation in the Game. I have used it for Buff Stacks Low HP and Ability Cooldowns many times over the years on various Characters. Blizzard added similar Visual Warnings in Cataclysm.Git Repository: https://github.com/Geigerkind/ModifiedPowerAuras
If you're looking for simple, just get actionator. Set it to undercut everything you post for 1c and alt click from your bags. It will place the item on the ah window, do a scan for that item and autoset the price for how much you told to undercut (you can change it accordingly if you feel like it). It will remember if you do stacks for which items and replicate it everytime.