There are many factors that come into play when deciding how much you will pay for a 2006 Kenworth t800. One is the miles and if there is something wrong with the vehicle or if it is in great condition. Online research shows they are from 27,000 to almost 40,000 depending on miles and condition of the truck. Once you know the details of the vehicle you can go to kellybluebook.com and they can give you an amount of the blue book value so you know not to overpay for the vehicle in anyway. But with all vehicle purchases making sure you know what you are getting for the price is important.