how to get item price from vendor?

hey guys... ive got a simple addon what shows me "ItemLevel: xx" in itemwindow...
so id like to get there extra line with "ItemPrice: xxg xxs xxb"
the price should be from the vendor (if i sell anything to another vendor so that price)...

i dont think it would be so hard to make the addon... for anybody who know how the language works (im programming PHP etc, not this language)

so the file is here (ItemLevel.lua)

function ItemLevel_AddInfo(tooltip, link)
if tooltip and link then
local found, _, id = string.find(link, "item:(%d+)%:%d+%:%d+%:%d+");
if found then
local name, link, rarity, level, requiredlevel, class, subclass, stacksize, inventorytype, icon = GetItemInfo(id);

if name then
tooltip:AddLine("ItemLevel: ".. level);
tooltip:Show();
end
end
end
end

function ItemLevel_SetBagItem(tooltip, bag, itemslot)
local hasCooldown, repairCost = tooltip:ItemLevel_SetBagItem(bag, itemslot);
local link = GetContainerItemLink(bag, itemslot);

ItemLevel_AddInfo(tooltip, link);

return hasCooldown, repairCost;
end

function ItemLevel_SetHyperlink(tooltip, link)
tooltip:ItemLevel_SetHyperlink(link);

ItemLevel_AddInfo(tooltip, link);
end

function ItemLevel_SetInventoryItem(tooltip, unit, slot)
local hasItem, hasCooldown, repairCost = tooltip:ItemLevel_SetInventoryItem(unit, slot);
local link = GetInventoryItemLink(unit, slot);

ItemLevel_AddInfo(tooltip, link);

return hasItem, hasCooldown, repairCost;
end

function ItemLevel_SetAuctionItem(tooltip, type, index)
tooltip:ItemLevel_SetAuctionItem(type, index);
local link = GetAuctionItemLink(type, index);
ItemLevel_AddInfo(tooltip, link);

end

function ItemLevel_SetLootItem(tooltip, slot)
tooltip:ItemLevel_SetLootItem(slot);
local link = GetLootSlotLink(slot);
ItemLevel_AddInfo(tooltip, link);
end

function ItemLevel_SetMerchantItem(tooltip, index)
tooltip:ItemLevel_SetMerchantItem(index);
local link = GetMerchantItemLink(index);
ItemLevel_AddInfo(tooltip, link);
end

ItemRefTooltip.ItemLevel_SetHyperlink = ItemRefTooltip.SetHyperlink;
ItemRefTooltip.SetHyperlink = ItemLevel_SetHyperlink;

GameTooltip.ItemLevel_SetHyperlink = GameTooltip.SetHyperlink;
GameTooltip.SetHyperlink = ItemLevel_SetHyperlink;

GameTooltip.ItemLevel_SetBagItem = GameTooltip.SetBagItem;
GameTooltip.SetBagItem = ItemLevel_SetBagItem;

GameTooltip.ItemLevel_SetInventoryItem = GameTooltip.SetInventoryItem;
GameTooltip.SetInventoryItem = ItemLevel_SetInventoryItem;

GameTooltip.ItemLevel_SetAuctionItem = GameTooltip.SetAuctionItem;
GameTooltip.SetAuctionItem = ItemLevel_SetAuctionItem;

GameTooltip.ItemLevel_SetLootItem = GameTooltip.SetLootItem;
GameTooltip.SetLootItem = ItemLevel_SetLootItem;

GameTooltip.ItemLevel_SetMerchantItem = GameTooltip.SetMerchantItem;
GameTooltip.SetMerchantItem = ItemLevel_SetMerchantItem;

Informant inside auctioneers addon pack gives you this and more information in a sub-tooltip style thingy under items you click on.

link:
http//www.auctioneeraddon.com (Auctioneer's Official Site)

a few mins ago i read from a curse dev that ColaLight on wowace.com does the same about.