I don't know where to get the metal and hardware parts cheap. But if you think about it, eliminating the cheapest part of this package (the plastic) probably isn't gonna save you much money.
I had a hard time accepting the purchase price of my Barkbusters too. But once I got them fitted, great fit and very stout, I was glad I spent the extra money over something like the Trackside guards. Just so you know, the Barkbusters also include 2 pieces of plastic per side, the part that attaches to the bar and a smaller piece that adds like an inch and a half to the shield. So when summer rolls around I'll take that extra piece off.