Finding the value of a lot in the San Jose area can be a bit difficult as open lots are few. A comparative market analysis is one of the most common ways of determining value. A comparative analysis would compare the lot in question with other lots in the area which have sold. Since lots aren't common in San Jose, I would also suggest taking a look at recently sold homes that were purchased and then fully remodelled or completely torn down and rebuilt.
If you would like some assistance in gathering data, I would be happy to help. Feel free to send me a quick email (April@AprilTavares.com) with the details of the property and I can see what I can pull up for comparable sales.