I would say a salvage title is a 25% discount to a non salvage title, depending on the damage of course.

At the end of the day, these trucks are very old and not worth much and doesn't take very much to total one out so the damage is likely be very minor. One dented fender and they are probably totaled.

Assuming they drive OK, and any repairs appear well done, there probably isn't going to be very much to worry about from a salvage title versus a non-salvage title. Overall condition, and how they drive, is a much bigger factor than title. Most of the ones I see for sale are either pretty trashed, and I wouldn't buy them regardless of clean title since they have clearly been abused, or they are sort of in good condition, and the sellers wants a huge premium, which is kind of stupid to pay given their age.