I reside at 06C and it's all GA. Don't know the tie down fees, but doubt it is excessive; Fuel is reasonable. Outside of rush hour, it is only a 25 minutes drive to ORD. PWK is probably closer, but based upon fuel prices, I wouldn't call it GA friendly. I expect ramp fees are much higher. It is only 10-15 minutes closer to ORD. No car rental onsite at 06C, but there is an Enterprise only a mile or two away. A cab to ORD is about $35-40.
Larry