That price is probably for the whole door frame with rocker panels. Look at LMC Trucks as they have replacement rocker panels and cab corners. You can cut out the old with a plasma cutter and weld in replacements and just paint with bedliner material. Unfortunately you will have more rust issues with this vintage GM truck. I speak from experience. Rear bumper rusting through, brake lines rusting, rear shackles, brake bleeders, trans linkage and lines are some of the issues I dealt with on a 2000. Final straw was frame rusting out at the support for the carrier bearing and the universals and driveshaft rusting. I have seen many of these trucks of this generation with some of this issues. You must decide if it is worth the effort.
Doug