How much does it cost to park for 3 months? International long term parking

I have not parked at OHare, but I would recommend a limo / taxi service as it would be far cheaper than parking for that duration.

I'm not sure about the long term parking, sorry.

I am not familiar with parking at Ohara

Im not sure but I recommended you, try to find different parking lots near the airport. They give you transportation from/to airport and is cheaper than the airport