After Effects Alternative for Windows I use Sony Vegas for video production but would like to be able to create more visual effects. 

Are there any cheaper alternatives for Adobe's After Effects? Or is there an extension for Vegas?
Blender does have compositing capability, and can be used to do some of the stuff that AE does. It's free, but you have to learn how to use it, so how highly you value your time counts in the final equation.

If you want to see Blender in action as a compositor you can see the "Tears of Steel" short film made with Blender last year.