That's a scenerio that many will face. Personally I dumped all my post ban uppers a couple months ago now. I traded them on a Preban Chinese AK. My justification for doing so was that:
A) To retrofit the FSB and thread the barrel + add a FS would cost a significant portion of the uppers value. (Also, if not done by someone with skill- it may damage a perfectly serviceable upper) So if I could get good trade now for the post ban uppers, I figured might as well take a small hit in getting something that I truly want.
B) The Preban Chinese AK will take a minimal hit in value as the 89 import ban will still be in place. The PB AK was all that I wanted NOW.
c) If the ban goes away and I later wished to trade the uppers on an evil correct upper the hit would again be substantial.
So I ended up trading the uppers off, keeping a lower and within a month I will know which route to go concerning uppers. I'm thinking M4 configuration and addinga collapsible stock....
I would not be able to justify $75 for a replacement FSB.... However, YMMV. As I see it, if it costs $75 for the FSB install + another $75(?) for the barrel to be threaded- it would seem to me that there will be folks willing to take a post ban upper + $150 +/- for a new Pre ban upper after the ban.
Sly