Yeah I understand where you're coming from as I'm just returning myself. But usually the most expensive pieces will fit into a few builds, such as sampires, bards, mages, tamers. Using rings/bracelets as an example a tamer/mage won't need HCI, DCI, stamina/dex, and SSI. Instead opting for MR, Int, LMC/LRC, luck, and FC/FCR. This isn't an all inclusive list by any means. And sometimes someone may pay top dollar for something unusual so keep an eye out.
But in general I would simply go to each profession forum on here and see what the popular builds are needing (pvpers tend to pay a little more imho).