You have your chest pieces confused. The ones you turn in drop from the actual bosses, and are turned in with a Sunmote.
There are patterns for Engineering, BS'ing, LW'ing, Tailoring, and JC'ing. I'd really be surprised if any but the Engineering helms start appearing on the AH, and those simply because there are so few engineers and so many helm patterns, and I'd be surprised if any of them were less than around 5000g.