It’s a question often heard on trade or other channels, what can I sell this for, what’s it worth. There is no firm answer, worth is a relative thing, it depends on the realm, the time of day, the day of the week. Some items sell for more at the weekend, some are better mid-week. It also depends on where the game is on the patch cycle. Buff mats (gems, enchanting, food) always go for more in the first few weeks of new raiding content for example as all those pushing through need to get their new drops brought up to spec.
The ultimate answer is "Something is worth only what you can persuade someone else to pay for it", there is no intrinsic worth to anything in the virtual or real worlds that is not linked to someone else’s perception of what it is worth to them or what they believe they can sell it to someone else for.