Thank "Sandolkakos" for providing the info on item.Sdata here is the link to what to edit.
Now.. what he didnt explain was correctly pricing items. For example lets say you want to put something for 500k sell price. Hex for 500k would be "7A120". Well if you input that into item.Sdata your not going to be selling for 500k. The correct way to list prices is to reverse the price by every 2 bytes. "20 A1 07" would make the correct selling price of 500k.
Remember this must be done on the client version and also in database.
~Phish