I like this website. Just go to Disneyland (or Downtown Disney, DCA) click on the restaurant you want. Click on which menu (breakfast, lunch, supper) and it will bring up the menu and prices.
The best thing to do is to call the Disney Dine Line. Prices vary by season and meal. If you know that you are going a certain week they can tell you the exact price it will be. Breakfast is around $30+ per adult and tends to be around half the adult price for kids.