Just a little PSA here. I checked Amazon and Ebay and they both have sellers selling new and used copies as low as $3 + s/h. There are probably other stores that have some old copies too if you search for it, and, you can always post in the classifieds of various hardware and gaming forums like Anandtech or Toms Hardware, etc.
Some cities also have used video game stores and you may find a copy there. I suppose used copies are a risk with the id/pw thing, but this game is worth the risk. I mean, if I lost my, copy, honestly, I would have no problem dropping $100 for a new one ( assuming I had the money). It's that good.
Make sure you specify the PC version, as they made it for consoles too.