KBB is good. banks at least here in Utah, use NADA to determine a vehicles value. The problem with vehicles as you know. They depreciate and the big tires and lifts don't add value in my opinion. That's money you're not going to get back. The rust isn't a big deal. As long as there is no mechanical problems. Its still in what KBB calls " good " condition. I've got rust on my back fenders, my truck is still worth $8000 according to KBB- good condition. But the biggest thing is. Shes free of major and and basically small mechanical problems. Cosmetics, at least to me is the least of my worries. Its a 13 year old truck. Mines 15 years old. Your gonna find plenty of Cosmetic problems. With yours being a mega cab, its basically a 3/4 ton. Its just a guess, you will have to run the numbers. Id say your truck is probably worth around $11000‐$13000. I also could be way off.