How big would a web search index be to be able to run it localy

I was just reading another thread about Google and Microsoft using our search against us in the ad wars, and was wondering how big an index would need to be for us to just have one local.

I wouldn't even care about the long tail, just say the top 10k web sites would do I think.

I wouldn't try and build it local by crawling, Id be happy to just download a big torrent an somehow patch it every week or so.