A factory Parts and Illustration Catalog is the best but it is hard to find them for multiple years. I have access to a 1994 C/K Catalog and it is great for use on my 93 GMC. I did find this site
http://www.auto-parts-for-less.com/chevrolet/chevy.htm You can get prices for GM parts but they don't give part numbers. I don't know what prices you have found but they have the inner track for $50.85 and the outer for $63.20.