Only you can answer that question. Every servers economy is different. On my server you lose 10g to smelt ore into bars. But if you farm as much as I do, you have to do a multitude of things with your ore. Ex.. I sell 20 stacks of ore, 10 stacks of bars, and prospect the rest selling the infernal gems, and then converting the green gems to rings for disenchanting. It's tedious work but its worth it. There are even profiles out there that will automate just about everything mentioned above.