A post over at JMTC titled "Cheep Greater Planner Essence," provided some decent information on getting greater planner essence cheeply, but the overall post fell short in some areas.
One of those area's is it listed some cloth armor amoung others that can be dis-enchanted into greater planner essences but isn't something to bank on.
An example listed was netherweave boots listed for 7g each on the auction house and greater planner essence going for 29g. Taking these figures lets break this down.
Netherweave boots have a 74% chance to dis-enchant into 2-10 arcane dust, 22% chance of dis-enchanting into 1-5 greater planar essence, and a ~3% to dis-enchant into 1-3 large prismatic shards.
According to a spreadsheet I put together that further broke down the chance of getting materials, you would at least need to buy 3 of these boots in order get at least 1 greater planar essence, this of course is if the RNG is on your side. If the RNG is not on your side you might at least end up with 7-8 arcane dust at about ~2g 69s each.
The Undermine Journal shows arcane dust on my server's market price at 3g 95s so in wost case scenario that is still maybe 10g 60s in profit for the dust, and or maybe 8g profit on a greater planar essence, Still a good deal, but should have been explained further, and looking for essences from armor isn't a good idea if you aren't taking into account the more likely outcome of dust.
Also when looking at weapons that disenchant into essences if you find some at around the mat cost that have a higher chance of dis-enchanting into one essence bank on one essence, if it has a greater chance to dis-enchant into two, then you can take a risk and bank on two.
Know the chance of getting each result using either Auctioneer's Enchantrix module or checking Wowhead for the item in question.
