Encrypt database data bundled with application

I'm building an application that bundles read only data for the customers to search.  Part of what the customer is paying for is the data, so I don't want them to have access to it directly, but I want them to be forced to use the application.  The main component of the app is a keyword search on one table (2 - 3 hundred thousand entries, each with a description up to 10,000 characters).  Based on the size of this data bundleing a .sdf with the app requires too much of a performance degradation.

So my questions are:  Is there a way to bundle the data so the user will not have to install additional software (ex. SQLExpress, MySQL)?, and How to deliver the data to the customer so that they can query it through the app but not be able to open the database directly.   From what I can gather if I use sqlexpress the user will be able to go through management studio to gain access, so if that's the best way is there a quick encryption/decryption technology built into .net that would not slow down my queries too much?  Is MySQL a better option?  Are there other options?