Your are most likely going to have to get a 15 passenger ford or chevy van.
These vans are usually not in the normal rental fleet but the commercial rental fleet and are priced accordingly. We needed to rent some and got them from
Enterprise.
When you first posted I thought you just wanted one for local WDW travel. Now that you post that its for a 2000 mile trip I think you are going to have to look into alternative travel like Air or maybe train (including the Autotrain).
These vans are generally used for short shuttle work and don't have many creature comforts like arm rests or bucket seats. Remember these vans are based on full size pickup trucks not cars and drive that way, 2 days down and two days back are going to take a toll.