The Deep Web is a nebulous beast of unknown size, so the answer to this is merely an educated guess.  Experts believe that 90% of Deep Web is searchable.

Put that in perspective, 90% of the Internet is Deep Web, and 90% of that can be searched. That means 90% of the internet is military, proprietary commercial databases, broke or just poorly designed.

Interesting that Google and Bing make a fortune dishing out the 10% they can index of the Surface Web. What does that mean you can do with the 90% you can pull out of the Deep Web?

To answer the question, I’ll estimate that 30% of the Deep Web is commercial databases and 20% military. I have no report to back that number up, it is merely a SWAG. So with that said, about 50% of the Deep Web can be searched for free with the right tools and determination.