ItemDataCache 

This addon provides both a static database and an active scanner for item data.

Note, this addon does not display gathered data by itself - it supplies data to other addons. For example if you want to see "sell to vendor" prices you've gathered, you have to install an Addon such as ItemNotes.

Features:
- Static "sell to vendor" prices database for ~30600 items.
- Active "sell to vendor" scanner that will save unknown or new prices for all items in your bags every time you visit a merchant.

Notes:
- Since this addon is currently in active development, there's no interface option yet to turn off messages, however ItemDataCache should report every item only once, so that shouldn't be much of a problem.
- *** WARNING! *** If you get repeated messages about same item on every visit to the vendor, that most likely means you've found some error in the scanner. Please report to me name of affected item and what properties (soulbound/quest/charges/etc) it has.
- If you really want to disable those messages, even considering that with current size of database you'll probably will not even see one in a week, you can use "/script ItemDataCacheLocal.Settings.noNewDataMessages=true" and "/script ItemDataCacheLocal.Settings.noUpdatedDataMessages=true" commands to do that. Note, however, that bug reports without information from those messages are much less useful to me and it will take more time to find and fix them, unless you'll be able to turn messages on again and reproduce the bug.
- This addon does nothing with collected data by itself, so you will most likely want to install one of addons that can display data collected by ItemDataCache or use it in its calculations:

* ItemNotes, display the price you can sell an item to in the items tooltip

* Informant from Auctioneer package: Informant's own database is updated periodically, but there are always some new unknown items or price changes. ItemDataCache hooks Informant.GetItem and inserts its own "sell to vendor" values. This allows Informant to display correct updated and previously unknown prices.

* BottomScanner from Auctioneer package: just like with Informant, BottomScanner's database sometimes do not have most recent prices. ItemDataCache will provide BottomScanner with prices it knows.

* Titan Panel - Itemized Deductions (ReBorn): this addon, created to help you free space in your bags by selling junk, dropping cheap items or combining incomplete stacks, uses ItemDataCache as primary source of prices.

* MobInfo-3: tracks information about monsters you fight, like their HP or what items they drop. ItemDataCache is one of alternative sources for item prices data displayed in tooltips and used in calculating total monster value for this addon.

* Greyprice: minimal solution to track your looting progress. This addon displays a small window with total cost of all the junk loot in your bags.

* SwitchRod: uses ItemDataCache class data to find fishing pole in bags and equip it on command or switches your equipment back.

* Additionally, any addon that uses either Informant (for example: GarbageFu) or GetSellValue API (for example: VendorBait) for item prices will work with ItemDataCache too.