Rather then trying to integrate fee in with the price on the item pages or user pages a simple AH fee calculator would be in order.
Perhaps a very simple page where you plug in the price you are planning to sell an item at. Also you would need a checkbox to say whether or not it is a stack.
The page tells you how much it would cost to sell the item from
(Jeuno / Nashmau / Tavnazia Auction Houses)
OR
(Al Zahbi Auction House)
OR
(Aht Urhgan Whitegate Auction House).
If you really wanted to fancy it up you could list out
(Item Cost) - (Listing Fee) = (Net Profit).
This might contribute to more people realizing Al Zahbi is cheaper, perhaps lowering a bit of congestion in AU-WG.