If you really want to choose a DB solution, then I would recommend sticking with what Apple recommends - CoreData. There is a learning curve, but there are some great docs on the developer portal which should get you up to speed quickly. CoreData abstracts the DB allowing you to save and retrieve objects rather than write a bunch of SQL.
You might instead wish to look at reading/writing files to the Application home directory. For more info, please look at the "iOS Application Programming Guide"which has a section on "Files and the File System". You could then persist your 500 files directly to flash, as opposed to using a DB/CoreData solution.
Files and the File System
Every application has a protected area
in which it can create and modify
files. In addition, the system allows
applications to share files with each
other (and with the user) through
well-defined and secure means.
However, supporting those means
requires work on your part. The
following sections describe the types
of file-related operations you can
perform in your applications.
Link to the programming guide:
http://developer.apple.com/iphone/library/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/StandardBehaviors/StandardBehaviors.html