I've also had the pleasure of working with John to produce a couple sets of custom headers and exhausts for my old Integra Type R race cars.
I paid $1800 for the first header, and about $1200 for the second ones that were slightly improved. He also did a custom exhaust for me, but it wasn't as nice as his headers. Fitment was bad.
Regardless, it was a protoype so I can't complain. The headers were very expensive but worth it in my opinion. With the help of his headers/exhaust, and some engine work/tuning, I was able to produce 240 HP to the wheels on an NA B18C5R motor. I was very impressed because all of the high dollar Japanese Headers didn't even come close to what his headers produced.
A friend of mine also works for John, so I can pass along his contact info for you if you want to talk to John about custom headers for your NSX...
-Michael.