30,000 mile service

Hi, I'm a new user, but I have heard about this site for a while. Anyway I have a 2005 Mazda 3i with about 31,600 miles. Tomorrow, I have scheduled the 30,000 mile service and I'm just curious about what others paid for it. The dealer quoted me $192.00 for basic service and then around $400-500 for any additional work. Is this fair? Also, lately I have seen a slight decline in my gas mileage, did anyone else have this problem and does the service fix this. (my next oil change was scheduled for about 31,655 so that's shouldnt be it and my tires are only a few months old)

Thanks