I needed one last fall and found that the 14085681 part number is discontinued from GM. (it was in the OEHQ.com catalog but when i ordered was told it was no longer available). I found one still in stock at a nearby Chevy dealer but even at the this-thing's-been-here-for-ten-years-and-we're-happy-to-get-rid-of-it discount it was still $100+.You can check with your local GM dealer. Here are the OEM part numbers for the molded hood insulation.
78-84 El Camino part # 12306178
85-87 El Camino part # 14085681