My wife loves to lecture me that it would have been cheaper to pay $10,000 for an overhauled, painted, good running, all the bugs out, M37 than to have paid $2,000 for one and then overhauled everything. But, look at all the fun I would have missed out on!
Seriously, depends on how you are going to use it (daily driver, long trips, parade rig, etc.) and if you can live with a few leaks, a little peeling paint, etc. Once in a while, a screaming deal comes along, but I would go with the following guidelines:
Parts truck- a few hundred dollars
Bad runner with rust - maybe up to $2000
Good runner, some issues but not much rust, up to $4000
Really nice, but not a show truck, up to maybe $8000
Show truck, all overhauled - saw one on Barret-Jackson go for over $50,000
These are just my ideas. Where I am, good paint will be over $5000. A full set of seals for axles, diffs, trans, xfer, winch, etc. will be a grand plus whaterver teardown costs are. Figure tires, brakes, rust repair, wiring, etc, etc. Then decide how nice you want to make it. And have a ball driving it and working on it.