you don't have to buy whole new doors, i think you can buy a kit. They have web sites you can go to. You might have to look around. I cant promise it will be cheap but they do have kits. On older models it would be harder to find doors for like your 89. Theres some on this link for your truck.
http://www.customautotrim.com/bodykits/lambo-doors/vertical_doors_products.htm?make=Chevy