The Commodore S has the standard headers as any other VN commodore V6.
The series 1 headers have pretty long runners though and are basically the exact same as a cheap header, e.g. Wildcat headers.
So basically buying cheap aftermarket headers will provide little gain in any area (performance or economy) over the stock headers, however a higher end brand such as Genie, Pacemaker, or HM will give you a noticeable gain in power, but nothing noticeable in economy.