The park's website does not post the prices. Most entrees range between $9 and $12, with a few specialty items (especially those at the Smokehouse) a few dollars more. Those specialty items are either not included in the all day plan, or are available for a small upcharge.
Like the poster said above, if you eat three meals, it's worth it. You can also get just a drink or snack at the participating locations as well, which ads to the value. It's definitely a better deal in the summer season when the park is open longer and more locations/service lines are open. If you eat two meals or eat light, you'll probably at best break even if not lose a little.