I'm think you are oversimplifying the problem. Web search is about the long tail you need breadth in your index. It will cost quite a bit more than a couple of bucks to do (storage is not that cheap, nor is cpu), and you'd have to do it repeatedly (and quickly as I mentioned above). And then of course you'll need enough computing power to perform the actual searches and run hadoop on your web index. There are only a handful of serious players in this space (check your site logs) for a reason