I agree with Therese, you can't assign a cost to a FIFO, LIFO, Average Cost, or Serial/Lot item until it is actually relieved from inventory. Until then, the cost may vary from when the entry is made, especially in sales order. If a quote or order is entered but the goods aren't shipped for another week or month, the actual cost of the item will most probably change between those two measurement points.
Miscellaneous items and special items are set based upon the cost when entered. However you run the risk of the cost being different if the cost is change at the item level between the time when the order line is entered and the sale is finalized.