CostcoCostco is selling 1-ounce platinum bars online for $1,090.The move comes about a year after the retail giant started selling gold bars and silver coins.Platinum prices are stable year to date but have risen 14% over the past year.Costco is diversifying its precious-metals business by selling 1-ounce bars of platinum for $1,090.The retailer is selling the item online, according to a web listing.According to the listing, the item, which is available only to Costco members, is 999.5 pure platinum and Swiss-made.