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You should be able to charge the hourly rate of salaried + 10%.
I'm not in Chicago but fairly close in a place with a lower price market, but my guess is you should be able to command $50-$75 per hour. Pitch $60 unless you have ungodly experience and then go high.
If they talk you down and you need the money, do what you need to do, but tell them to pound sand if they go below $40/hr. This is Chicago. There's money there but they're bung-h*les too.
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Azathoth
Son of Cthulhu
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