I would release two versions, like XP : Home and Professional.
I'd make Home $99 and Professional $199, and allow up to 4 activations, each. If you only have two computers at home, you already know at least two other people who want an upgrade. You could even charge those people the $20 or $40 and make your money back. Think about it, you could actually do something positive, and reduce piracy... even if just a little bit.