When I set the Valuation to Automatic in Category options then the Cost field in Product is read-only.

Now if I do an inventory adjustment or register manually a Transfer of products there is no way to enter the cost so the inventory value will be 0 (or whatever the field shows)

In V10 I can change the Cost before validating a transfer or inventory and the new products go to the stock with the new cost. The only way I find to controll the value of the stock is through PO where the purchase price is correctly taken into account.