I find it to be much more cost effective to just buy gear from the AH to DE rather than crafting it. The cloth costs too much and it makes no sense to go farm for the cloth when I can make more money just standing in front of the AH for a few mins every day.
For Illusion Dust, look up items level 56-60. You probably want to install the gamma version of enchantrix so that you can tell which items are old-world and will give Illusion Dust and which are new Outlands drops as those give Arcane Dust. 56-60 items give the most, then check the 51-55 items. Obviously you want to pay less for these as they give less dust.
Arcane dust I don't know exact numbers yet, so I'm not sure if the same level breakdown applies. I've been buying items 61-70 that cost 2.25g or less as they seem to give at least 2 Arcane Dust. Cheaper than buying it for 2g each from other people.
I know that didn't answer your question, but I just don't find crafting to DE to be worth it :)