The price solely depends on what you're willing to pay and what he's willing to accept. There's no guide or rule of thumb on these old trucks. Some people give them away and some think they are made of gold. I always haggle on the price. If he doesn't budge, I need to either pay or go away. I try to stay away from projects like the one you mention here because I'm too picky about my workmanship. I can't stand lazy or half-assed work and wouldn't trust it without redoing it myself. To each their own though,
Good luck,
Scott