I went and built my own set for a few reason...COST is a big one and figured my time wasn't nearly worth what others wanted for just piping. The other reason was that mine is custom (Cummins in a GMC) so there was nothing available. There was nothing for my combo of chargers I was using or in the configuration I was using (hood stack).
Gathering all the parts was the most time consuming and really it wasn't that expensive for everything. Granted I sourced all the parts my self and didn't reley on using pre-fabed parts from places like Source Automotive. In my system I have only $150 worth of steel and tubing and boots and we made out own flanges and everything. I have thought about selling the flange/4" adapter but not sure if anyone would be interested in it.
Here are some pics of my setup.