New 3/4 ton panels are $650 from LMC for 54-55. I haven't seen any manufacturers that list 1 ton replacement box sides, but I've heard they can make them for $$. If you're going to cut them down the 1 ton box is about a foot longer but DONT QUOTE ME as I'm only guessing. Someone who has the actual dimensions at hand will correct me. Also I'm not exactly sure where it is longer. It may be in front of the fender (harder to cut and splice) or maybe near the back (easier to cut and splice).
As for used (which I assume you purchased) it really depends on the condition. I had numerous dents, rust and holes in the used box sides that I was given because they were too much work. I instead used them as a template and for some parts to build my own replacements for about $1000 in materials. This included bed wood, polised stainless strips, new 16 gauge steel cut and bent (along with bent and cut 1/2 ton sides too), exhaust tubing for the top tube rail and a 2x6 tube for my back cross sill. . I used stake pockets from parts trucks to complete.
I recently acquired a 9 ft box requiring some work. I will be selling it and will "test the waters" so to speak as there are a lot of want ads around me for a set of box sides. I don't want to rip anyone off, but I don't want to sell myself short as they are harder to find in any decent shape.
