Congrats on new ride. I'm curious what your plans are for long term undercarriage protection. Even though I'm in the desert, we go to UTAh alot and salt really sucks. I've developed surface rust as well, sanded and used Rustoleum rubber coating but thinking should've used rock chip paint instead. You, however, will see more corrosion than we will here.
Price from NADA/Edmund's/KBB are really averages. Certain parts of country and the time of the purchase, and demand, dictate price. With gas prices low, full size trucks are not as cheap, used or new. Just like BB of GunValues...have NEVER seen a good antique Winchester lever action go for BB price here in the West (always more). The fact that your rig was one owner, low miles...that adds a premium in my book. BUT, 13 yrs old...consider changing all the rubber under the hood (coolant hoses) and change all fluids (PS, Brake, Coolant, differential(s) etc). Enjoy your ride. Our 02 Yuk with 165k is loved by my children...the most comfortable car they've ridden in.