Iam not sure that this work on all servers but it does on mine.
Buy Volatile Earth and Elementium Bars and smelt them into Hardened Elementium Bars and sell them for profit.
On my server it is:
1 stack of Elementium bars 200g
8 Volatile earth 120g
= 2 Hardened Elementium Bars.
The bars sell for 450g+
That means 290g profit/hardened elementium bar.
5800g profit per stack of hardened elementium bar.
It is repeatable as much as you want and on some servers like mine you can make massive amounts of gold since there is always volatile earth and elementium bars on the AH
As i said i dont know if this will work on other servers but atleast i tried.