Any parent knows that diapers for a newborn baby can be a huge expense. Child rearing information site babycenter.com estimates that the average baby's diapers cost about $1,100 in a single year [source: Baby Center]. At a warehouse store, or by waiting until your local grocery store has a sale before stocking up, you can save in the neighborhood of 25 to 35 percent of those costs, resulting in more than $350 in annual savings [source: Switchyard Media, Wallet Pop]. But don't let your purchases outpace your baby's growth and don't buy too many bulk packages all at once. Wait until your baby has just graduated to a new size to stock up.