...for free (I mean the carrier picks up the order and delivers your stamps at no extra charge). Just order the 90c stamps that way. 90c + a first class stamps (41c) and you are only losing a penny per.

http://shop.usps.com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=10152&storeId=10001&categoryId=11828&productId=29594&langId=-1