Congrats on the trip! I'm jealous... I can only manage to get 5 days for a road trip.
I'd sell the car and buy something more fuel efficient that will still serve all of your needs for both the trip, and normal driving. You're looking at a $6,800 fuel bill as it is. If you drove something that got 30mpg, your bill would be $4,100, or $2,700 less expensive.
What are you bringing that requires a rack? If it's just 2 people going, and the rear seat will be removed, perhaps you can fit everything inside the car. This will be more secure and save you tons of gas money.
Here's a guy that turned his Prius into a road trip champion by removing the rear seat and building in storage/sleeping space.