Airsoft guns look very real on camera.. and they have a much more realistic feel to them as well, compared to other 'toy' guns. I don't know about Chicago, but I know there's a guy here in the Twin Cities that runs a business called "Props on Wheels" and he brought out a cop car, lights, decals, everything to a shoot I was PAing on .. I talked to him a bit, and I guess he adjusts his fee based on the budget. He also said he can get any kind of vehicle (costs would reflect this though..) tanks, boats, planes, you name it.
I'm sure he'd travel to chicago if the price were right, but there's probably someone around there that does similar work.