Not sure if all of ORD is reasonable, but I know my boss used to complain that the ORD McDonalds cost less than our local (SF North Bay Area) McDonalds for the same thing...
ORD McD's is definitely higher than the city, probably 25%-50% depending on the item.
BAA (the operators of PIT) seems to implement this scheme in the airport terminals it takes over. IND is another example, plus I can get Chik-Fil-A.