The fees usually run from about $300 to $500, and then you'd have your travel expenses. But as a pitcher, you need to know you will only get a few innings usually 2 or 3. But it's well worthwhile if you think you can compete and are in top condition.
Being from California, there should be other resources for you that are closer to home. Maybe you should post in the California forum and see if there are any local showcases planned for this summer.
Good luck!
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"People ask me what I do in winter when there's no baseball. I'll tell you what I do. I stare out the window and wait for spring." Rogers Hornsby, Hall of Famer