Another reaon that they are in such bad shape is they were used as a truck and not regarded as being a sport truck or worth anything until recent years, so most of the 806 that were made have been driven into the ground.
I think mine is one of the cleanest around when i bought it, with only 53K miles and 2 owners, ran and drove fine, very minor rust in the back of the bed and drivers side fender, but it was in Boston Mass its whole life until i bought it and i paid alittle over 5 grand for it and flew to Boston and drove it home.
As far as value my insurance guy said to them its just a 92 GMC Sonoma nothing more or less, so when it gets back on the road ill most likely get some kind of agreed value coverage just to be safe.
One just sold on ebay for around 3 grand, and it had less than 70K miles and had all the cladding, was red and grey, and had an apillar pod and for some reason the owner before the guy that sold it mounted a volt guage in the glove box door, other than that it seemed to be a pretty clean truck, the bidding was started at 5 grand but after several days and no bids it was lowered to 2500 starting price. Like everything else they are worth what someone is willing to give for them.
Good luck with your search for a Sy/Ty.