As Math Geek points out, it's not the Media that costs anything. That can be downloaded at will from any number of reputable sources as often as you like. It's the product key that costs $99. Since Microsoft no longer sells Windows 7, there is no other place to legitimately purchase just the key. You'll need to purchase the full media disk; which basically means, you're purchasing a product key AND they're giving you the media as well.
-Wolf sends