Don't think you will find that - pricing is too volatile to have a site that would have a list of value.
- again its worth the amount someone will pay for it
No, you have to visit a few guilds and gain an idea. Fortunately, I shop for only certain items, not all items. So, after a few Guild Traders I pretty much know what the reasonable prices are, what the cheap prices are and what the ridiculous prices are. So, now if I see something that is at a cheap price, I buy it without trying to shop around. If I see something ridiculous, then I pass it by. If the price is reasonable, and I need it, I buy it.
For example, a traited item for research. If it's 200 Gold, I buy it, if its 300 to 500 Gold and I am going to be signing off the game soon, then I buy it and use it, not wasting the time to save a couple hundred gold. If it's more than 500 Gold, then I look for another one, I am not encouraging over pricing.
Enjoy the game, life is what you really want to be worried about.
PakKat "Everything was going well, until I died"
Gary Gravestink "I am glad you died, I needed the help"