Maintenance for the week of May 13:
• PC/Mac: No maintenance – May 13
• ESO Store and Account System for maintenance – May 14, 9:00AM EDT (13:00 UTC) - 12:00PM EDT (16:00 UTC)
If you're on PC, pick up the Master Merchant add-on. I'm assuming you're in at least one trade guild by your post, but if not, join a few and it will track the data of what people have sold items for previously, which should give you an idea of how much people will pay for it.