Welcome back Rip van Winkle.... Unfortunately while you were away, Mark McWillis of TROS started "back cutting" standard barrels for a threaded adapter, and the price of an extended length barrel in 9mm tumbled accordingly. You are looking at under $1K for that item, $800-$900 if you are lucky. Another factor here is that since the days when the P9S was the premier suppressed center fire platform, many manufacturers now offer at least one model available with threaded barrel from the factory, further impacting demand. Neither Mark nor Tornado Tech will back cut a .45 barrel though, barrel wall not thick enough, but still with the USP tactical and the Mk23 available, you would have to be the kind of guy who can take advantage of the P9S' fixed barrel accuracy or the fact that it is therefore reliable with any weight of can without a LID to care about that anymore.
Description-wise your listing implies that this barrel is a "factory threaded barrel" when in fact is a factory barrel that has been threaded. H&K doesn't do inch threads.
I have four 9mm 8" "Hunter' barrels waiting to immigrate. 10 years ago that would have been a big deal. No longer.
Sorry to be the messenger.......