Illusion dust usually sells for about 2g per, and greater eternal for 10-15g per, and this is a way to get both of them fairly easily! All you need is an enchanter (of course!) and a leatherworker or jewelcrafter.
If you have a leatherworker then create wicked leather headbands, they dissenchant into about 2 illusion dust or 1 greater eternal (or if your lucky then a large brilliant shard or even 2x greater eternal!)
If you have a jewelcrafter then create onslaught rings or sapphire pendant of winter night, both of these dissenchant into illusion dust or greater eternal essences, and I have occassionally seen about 5 of them in the ah for 1g! (really cheap i know, but if u can farm the mats for these items for a whole day... then it would be well worth it, im guessing you could make about 300-500 in a day if you had a 70 farming the mats)
Hope it helps you!