Whenever i go to the AH i always check the prices of greater essences (greater magic essence, greater astral assence etc.) and then i'll go and have a look at the lesser essences of those (lesser magic essence, greater astral essence). On my server I normally find that 3 lesser essences go for cheaper than 1 greater essence, and in case you didnt know 3 lesser essences = 1 greater one. So i go and buy 3 lesser ones, make it into a greater one and sell it off for cheaper than the rest of the greater ones and make a good profit off it when done in bulk ^^. I hope this helps you guys as much as it has for me