USPS will send you the boxes,tape,labels,confirmation slips all free of charge.Just go to www.USPS.com and place an order,usually takes a while to get the order though.
Also you can print out labels with postage(using credit card)or without postage at:
https://sss-web.usps.com/ds/jsps/index.jsp
Delivery confirmation is free if you print out with prepaid postage.