So many variables...$20 for 4oz? $20 for 5.5 oz? 4 oz of a triple milled soap should last far longer than 4oz of a croap...I personally am shooting for no more than $5/oz, but I'd be flexible in some cases if need be.
+1
Unit price is a better way of looking at it. A Kg. of P160 would be the equivalent of about nine 4oz. tubs.