What poorboy said is true and it also depends on the appearance or style you're after.

For my 37 pickup, I wanted something that appeared as stock as possible and, I didn't want to spend a small fortune getting it. I bought a bench seat frame from the wrecking yard that I removed from a Mazda B2200 pickup ($15). I liked it because had a nice tube steel structure and was close to being usable as it was. Then because of the narrow width and taper of my cab, I cut the seat width and narrowed it, followed by "pinching" it to get the same taper as my cab. It worked out very well and looks great.