As already mentioned, it's all in what you start with and what you expect in the end. That being said.
I bought an Arizone blazer that was being sold as "rust free" but ended up needing about 2K just in body work/repairs. Then it cost somewhere around 4K for the paint job. A really nice base/clear paint job but still 4K.
Adding that to the cost of the blazer totals roughly 12K but with everything spent on it I'd say closer to 13K.
I'm actually happy about that number, it turned out pretty good and I'm happy with it.
Typically the previous owners are our worst nightmares. There was a thread about them awhile back, some very scary stuff has been done to these trucks.
You have to remember, once upon a time these were just trucks and driven that way on a daily bases.
Good luck and keep us up to date on you project.