The last two I had, I sold for $100-$150. $400-$600 is definitely in my view of 'silly money'. They're ok but there's certainly more effective/functional braces out there (even beyond what we offer).
@shadycourgette , you asked a question about the Ultra Racing swaybar offering earlier and I missed it and didnt provide a response.
In short, their rear bar is pretty good and would be my preference (now) over the IPD offering. Back in maybe 2014/2015, we'd been looking at reselling them. We got an eval P80 rear bar and fitted it to my 1998 V70T5. Finish was 'ok' but not brilliant and it required minor modification to fit. Unless you have a hoist and were ok with taking a grinder to a brand new bar to make it fit, you might have been unhappy.
From a reseller viewpoint, while the bar we got may have been an exception, this made me lose interest in taking them on to resell.
Fast forward some time, all of the Ultra Racing swaybars I've seen since then (with no exceptions) had nicer welding than the one we got and I havent heard of anyone who the issues we had. Maybe we got a 'friday' bar.
I may reach out to them again and buy one in to eval it again to see if the experience is better this time around, being 7-8 years later.
