Decently priced one way rental?

[3princesses+aprince]

I think we'll be driving to Disney in September and the cheapest car rental I can find is from hotwire for $800.00. That is not too bad considering it will be a 12 day rental. Then I figured i'd check for one way rentals, this way we could drive there, drop off the rental and then pick one back up for our drive home. I just don't think we'll need a rental car to sit there all week. But that ends up costing more than the 12 day rental. Am I doing something wrong. Does anyone know why that is?

I do have a Ford Explorer, so it is always an option for us to drive our own, i'd just rather not worry about mileage on it and anything else happening while we're driving.