Excess Potion of Accelerated Learning: Acquired in your Garrison (part of the Warlords of Draenor expansion), this gives you a 20-percent bonus to experience from killing monsters and finishing quests. It lasts one hour, but you can buy it multiple times and use it back-to-back. Alliance players buy it from Sergeant Crowler, horde players buy it from Sergeant Grimjaw. Does not work above level 99.
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.