Not knowing what year your rig is (or what you even have, for that matter), if it's old enough to find more than one in the junk yard it's likely that it's also old enough that the only place you'll find body-parts is the junk yard.

As is the case with pretty-much most of us on here, if you want parts like those, and you want to reduce costs, you either have to find one on a junker and do the work yourself or you have to get lucky with a private-party seller.

If you have a newer rig, then you'll have to pay to get it new or (again) from a private seller or a junker if you could find it. In any case, the more work you do yourself the less it'll cost out-of-pocket.