I built mine from sections of straight tubing, select mandrel bends, and custom header flanges and disconnect flanges i made. With a pair of flowmaster 50 series big block mufflers (huge!), i figured i had about $600 in it, not counting my fab and welding. This was maybe fifteen years ago. The mufflers are now twice what i paid , ($200 each now?!) im sure the tubing and bends are too. But, with some extra flanges i made, and some leftovers tubing, i bought two hooker aeros (cheapest real muffler with 3.5 in and out) for $50 each, so i had a full 3.5 system to the axle for my cortina for $100.
If i were doing it again today..... i'd buy a 3" stainless system from jegs or summit, with their house flowmaster copy's, maybe have less then $350 in it, and make my own h-pipe.
Just a side note, my 3 1/2 system to the back bumper with bigblock flowmasters is almost a hundred pounds. Street car with exhaust and steelies, to bracket car with light wheels, slicks and exhaust removed, well over 150 lbs lighter.