Sorry to disappoint you, but this (and in fact any others of this kind) is unfeasible.
- No one has systematic access to transaction prices
- Outspark may well implement auction
- Insufficient labour power to make wiki-style updates
Just to give an example of how it might work, the
grand exchange of Runescape is an interesting one. However, that has the blessing of being integrated into the transaction process of every single trade through the system.
Suggestions involving this type of intimacy with game servers are best directed to
here.