The way that i farmed these dust was simple, i just done all the quests in Northrend and disenchanted all the items i got (excluding the items i used to increase the stats on my character), i managed to farm 30+ stacks of  infinite dust  and about 20 stacks of the greater cosmic essence and a few stacks of dream shards from the quests. i also do tailoring and disenchanted the trash green gear that i made to lvl that up, this gave me a few more stacks. this way i got my enchanting up very fast and did the acheivement and got the pattern for the epic cloak in tailoring. so in my opinion this is the most cost effective way to lvl enchnating up. happy questing