This site gives the price from last summer
http://www.themouseforless.com/tripplanning/menus/dl/Goofy.shtml
About $35 for adults for breakfast and $17 for kids. That's not as much as I thought as the other character breakfasts are pretty close to that.
Shows dinner as about $40 for an adult. Be aware that the prices fluctuate by time of year and can rise every year. Also you have to pay tax and gratuity too. You can call the dine line and ask the price for your dates before making your reservation.