Here is a free, open source non linear editor called Lightworks. However, the workflow is much different than editors like Adobe Premiere or Final Cut. It doesn't come with HD codec support in the free version.
Even if you want the HD codec the "pro" license of the software is only $60.
If you can understand and embrace the workflow logic which they use, which I believe is similar to Avid, then you should be in business.
It is a fully-developed platform which has been and is still used in the movie industry.