FAH/AC systems are pretty expensive...
If you mean the price of the item, then there are quite a few. The godly mace of the ancients is the most expensive weapon. It cost 1,000,000 coins. The Tentacles of the Overlord is the most expensive cape. It also costs 1,000,000 coins. The last most expensive item that I know of is the is the Pile of Gold house item. It costs 1,000,000 coins as well.
The most expensive fashion item is Marilyn Monroe's "Happy Birthday Mr. President" Dress. It was sold in 1999 with a winning bid of $1,267,500.
A hello kitty purse
T-Swizzle.
By Air
The most expensive item is the Wittelsbach-Graff Diamond valued at 23,400,000.
The most expensive Nintedo item is the Nintendo Wii with all it's games and the motion locator
The entree usually, though some deserts can be very expensive.
The most Expensive Item I have heard about is called the "Legndary Foe Cannibal". It can be sold for almost 13 million dollors!
In "The Elder Scrolls IV: Oblivion," the most expensive item is the Master's Mortar & Pestle, which is an alchemical apparatus. It is valued at 50,000 gold, making it the most valuable non-unique item in the game.
The butler