Bedroom in the basement, anybody know the codes? (Illinois)

[Jim B.]

I'm about to go under contract for a home in the West Chicago Burbs and want to potentially add a bedroom to the unfinished basement, but I'm worried I may (probably) have to add an egress window in order for it to be legal, especially for a rental.

Does anybody have any input on this?  I know it varies a lot by state and even county or city, but wanted to know if anybody had experience, specifically in the Chicago area.  

Also, what would you estimate something like that would cost?  I'm thinking at least a couple thousand...