How Much Does it cost to change last name in city of chicago?

I am wondering how much it would cost in chicago to change last name... I wanna change it do to the fact i wanna carry my grandfathers last name it ends with my mom and wanna change the name to carry it on. can anyone let me know how much it is?How Much Does it cost to change last name in city of chicago?Google Free Legal advice and there should be several links. They can probably give you an approximate answer or call an attorney in the Chicago area. I have used the free legal advice site before and you get an answer within 24 hours.