Here's a cheaper "Snoozer seat" that I found for $29.99:
http://www.wag.com/dog/p/solvit-taga...7&kpid=QZK-015
Since it seems like you're leaving tomorrow, you might want to take a trip to the pet store to find one of these...they look super comfy and might make the experience for your pup easier.
Try to socialize with your pup for about 15 minutes before taking him/her on the long road trip, it might put your pup more at ease.
Try to make this car ride as pleasant and non-stressful as possible, to avoid having your pup develop a fear of the car.