A significant cost for efficient headers is due to the highly effective, and fully patened Burns Collector.
Some builders make a modified collector to get around the collector, but this hidden item raises the costs a bunch.
Just the fact that you must obtain Vipers of various years to properly fit headers is another big cost. Design must allow for fairly equal lengths prior to the merge. Installation must be considered, longevity, multiple dyno runs etc.
Jigs must be built, welding equipment and trained operators sourced. Dyno runs must be performed to determine optimum design. Then when you get them built you must market, warranty, ship, and continue to develop new models.
My first set of SVSi headers brought tears to my eyes the first time I took power laps at Willow Springs. The sound and fury went a long way to fulfilling my Walter Mitty dream of driving a race car.