It depends on what you can do yourself and what you will have to pay someone else to do. Im doing 99% of the restoration on my truck myself (engine, interior, paint, wiring). Anything else (any welding, exhaust) will be done by friends for little to no money involved.
The cost will depend also on what kind of resto. If you just want it to look and run good, or a 100 point resto, that can get very expensive.
IMO, the drivetrain will be the most expensive, if you pay someone else to do it. Machining and head work will make up a lot of that cost. The actual rebuilding can be done yourself if you even have decent mechanical skills.
The real cost will be in all the little things that add up, such as you may think thats a small dent on the fender, but it might be a lot worse if someone did a bad bondo job before you got the truck and you have to strip it all off and start over again. If you do it yourself it means it will take a lot longer than you expected. If you pay someone, then its big bucks. Or you decide to rewire the radio and realise that all the wiring under the dash is shot and needs to be replaced. If your gonna do that, you might as well rewire the whole truck, its old enough to need it. Neither jobs are really that hard if you take your time and learn as much as you can before you start it.
Get a few books on restoring cars or trucks. No matter what vehicle is being restored in the book, there are still plenty of tips and info you can use for your own truck. Buy books on engine rebuilding, electrical systems, and bodywork.
Surf Ebay. I have saved so much money buying parts from there. I got a brand new radiator for $10, a factory 4 barrel intake for $40, and a full gasket set for $45. Plenty of deals to be had there.
It can be a fun project, and if you shop around and get the good deals, it wont be that expensive either. I went into my restoration fully knowing what Im getting into, and I expect to put about 10K into my truck to make it magazine worthy. I also know it might be double that before I am actually done. I got lucky in that my truck is solid, no rust and is 100% complete. It runs so I dont HAVE to rebuild the motor, but Im going to anyway. I drove it for 7 years so I know all the little quirks and problems it had before, so there will be little or no suprises.
Good luck and have fun. The more work you do yourself, the more you will appreciate the effort when its all done.