The best you can do is be smart about where you spend money, and make sure that you never spend TWICE for the parts.
My own observation is that there is an exponential increase in costs based on the tire size you want to run.... 33" can be reasonable to build because you don't need to swap axles and don't need much lift or HP to move it don't the road. 35" gets more expensive because you need new gearing, more lift and probably some axle upgrades for strength....
At 37" and above the costs go completely non-linear. More lift, new axles, more power, more expensive driveshafts, crossover steering, hydro-assist, etc. Forget about budget when you get to this point.....you're screwed!
The hardest thing is deciding if you are willing to have a "driver quality" truck or you want it to be truly 100% perfect with all the rust repaired.
Realistically, a complete "stock" restoration will probably end up costing you $30,000.... If you want "upgrades" just add those to the total cost. Most people are completely unrealistic about what the costs involved really are, and end up frustrated that they can't get the truck finished for $10,000.
That's not to say that you can't have an enjoyable truck for less, but you have to accept some compromises and pick your battles.
-G