I bought the collectors a few years back and paid about 8 dollars each or around 5 pound if my conversion is accurate. I would imagine they are more now, not much ever goes down in price.
The header tubing was about 40 dollars or around 25 pound.
The flanges I am not sure as it was scrap I had, I didn't pay much for it.
The 2 inch side exhaust pipe on the was 32 dollars or about 20 pound and the mufflers were 50 dollars for the pair or around 32 pounds, assuming my conversion is close, another 32 dollars (20 pound) for stainless V clamps.
I guess a little more than the 150 bucks mentioned earlier, closer to 170 dollars.
It was one of the more fun parts of the car as far as build goes.

Al