Pride Parking. Cheap and van service is prompt. The longer you stay the cheaper the rate. Its around $6.50 a night for 4 days or more. Outside parking though and kind of a small area so reserve ahead of time on their website. Pay cash its cheaper. Also the Quality Inn O'hare has crew rates ( About 35 a night). It is right across the street from Pride parking. Its a dump but for commuting it works. Also they let you park there for around $8 a night I believe even if you are not staying at the hotel. Good luck.