Where is the best place to rent a car for 6 months?
(In Madison, Wisconsin)
Most of the majors do have a long term program. I would shop it across several of them. Plan on around $1,000-$1,500/month probably.
Two key caveats to watch for. First, look at the allowable mileage and the overage per mile. Make sure you will be within that. Secondly, look at insurance options. Most of the additional coverages will likely still be priced on a daily basis and that could add up to two or three times the cost of the car itself. Doubtful if any credit card coverage you have would apply.
You can price rentals directly on any of the major car rental company websites.