Staples is offering Microsoft Windows 8 Professional 32/64-Bit Upgrade (Boxed), model no. 3UR-00001, for $69.99. Coupon code 41793 cuts it to $39.99. with free shipping. Sales tax is added where applicable. Deal ends October 27th, 2012.
Of note, in-store shoppers can get the same discount with this printable coupon: http://reg.e.staples.com/c/s/tagfrm/hBQiqXsB7SHGCB8u1EfNsloBJQt/coupon.html?PID=552179&COUPON_1=47586&CID=AFF%253A552179%253A552179%253A10428703&n=9821&cm_mmc=CJ-_-552179-_-552179-_-10428703&email=staplescoupon%40staples.com&SID=VUlycWZRb0JDamNBQUg0eThGZ0FBQUxs&AID=10428703&storeId=10001