They're out there. They can be hard to find just due to the age of them now.
I've had 3 of them, at one time.
Blue, red & maroon.
Usually get them from private individuals parting out these trucks. The seats don't seem to last too long in the wreckers. The Fat-Fendered HotRodders & the C-10 guys like 'em, so they get scooped up pretty quick.
I'll pay $100-$150 for one in average shape, and no more than $200 for a really nice one.
This one would be in the $100-$125 range just because of the staining on the passenger cushion & the foam on the cushion's outer driver side edge is needing a rebuild.
A $200 seat would be one that can be bolted right in without requiring any work.
Because GM in their infinite wisdom decided to glue the covers right to the base foam, they are a major PitA to do be doing any stitch work to. Damn covers have to be pealed back like skinning a moose. Inch by inch with razor knives & lots of steam. (softens the glue)
It takes almost the same amount of time just to get the covers off of the seat faces as there is in stitching up a complete new set of covers afterwards.
The base foam rebuilding work is pretty easy. Only requires the outer bands of the seat to be rolled up so as to be able to get to the foam. Doesn't require removal of the covers from the foam faces themselves.
Sent to a shop to get done, recovering can get expensive just due to that amount of time it takes to get the covers off.
Not only that, roll-stock of original matching fabric just doesn't exist. Even when GM still stocked it, it was limited in supply & stupid expensive.
So fabric condition is important if you're not figuring on the expense of recovering, & that fabric condition takes precedence over any other probs such as dead foam, broken frames &/or tracks. That stuff is an easy fix comparably.
Good thing is, the material is tougher than nails & lasts & lasts & lasts. Most can be cleaned up & fixed up to look very presentable with a minimum of work.
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