I don't think there is much advantage to buying an upgrade copy anymore, just buy a regular OEM copy. Here's Windows 7 Home Premium for $116. A retail upgrade is $125.00 at NCIX. Retail is better for moving your copy from one computer to another.
http://www.ncix.com/products/index.p...t&promoid=1030
You can also buy the retail family pack upgrade for $200.00. This gives you three copies.
Another option if you are comfortable with this, is to buy a key on the net and download and than burn a DVD copy or find a friends copy.
http://trustpayjsc.com/categories/Operating-System/