eBay is a great place for deals. (And no, I'm not talking about bootlegged software.) I got a copy of Ulead VideoStudio 9 on eBay for $30. Intact, in the box, ready to be registered.
There are also good deals on older versions of Sony Vegas Movie Studio and Premiere Elements. It'll cost a few bucks, but nowhere near full price, and they're TONS better than Windows Movie Maker.