Many years ago I contacted various car rental locations in both the starting and ending locations to see if they needed any vehicles moved, surplus at starting location, low inventory at destination. You might spend a lot of time on the phone or computer asking and find nothing, but sometimes you can get lucky and find a company needing a vehicle moved, and you can get a very good deal. Usually normal car rental companies, but could also be U-Haul, Enterprise or even a car dealership needing to transport a used vehicle to another location. If you have the patience, there might be something out there, but trying to find something that seats 6 might be a tall order.