Where do you live? If you live anywhere but the west coast or down south this undercarriage rust is nothing and shouldn't scare you away from a good vehicle, if everything else checks out. My 100 spent its entire life in the north. I owned it for 16 years and drove it 331k miles and the bottom looked a lot worse than this. I never had a single issue with the truck due to rust.
Now, if we were talking about body rust I would recommend keep looking. But chassis or suspension rust? No big deal.
The real deal is to find a truck with an extensive service history, that was loved and maintained by its previous owner(s).
Yep.
My 2001 lived it's whole life in New England and is doing great!
I was pretty vigilant about doing the oil undercoating prior to the winter months. The guy uses new hydraulic oil and sprays the entire underside as well as the cavities in the rockers and lower doors.
It's a bit of a mess for the mechanic to deal with, but I'm sure they prefer a little bit of oil to having to use the "flame wrench" every time they want to remove a bolt!!!!
Some areas of mine are showing some surface rust again. I'm tempted to do some careful wire brushing and hit those spots with a rust converter or zinc chromate (if I can get the metal clean enough).... then topcoat with a nice Eastwood Chassis Black. Mostly, just to improve the cosmetic appearance of things like the lower control arms, lower shock mounts.... basically, the stuff that is visible when you step back and look at the overall appearance of the truck.
-G