best power conditioners under 4k

Right. But not for the reasons you think. You're still getting noise from your appliances, and everything else for that matter. All that happened was you improved that one little thing.

Improved a major issue to the noise floor. I'm living in an old rowhome in an old neighborhood with shared lines, shared transformer and ungrounded houses.

Of course, appliances are adding noise; they're wired to the panel on both legs. Tweaks could be used here, but right now I'm satisfied with the improvement.

I loved my BPT and Audience, but liked it better when I removed them months later...

Unsure about 'best' option, but the Decware ZLC works well, is about 1K shipped and returnable.  Spending copious quantities does not ensure results.

The Inakustik AC-3500p has done an amazing job in my system. The difference between it "being in the system" vs "not being in the system" is significant. For me it is a worthwhile investment and the price is less than the budget you have set.
Check out the thread on this power conditioner, here on Audiogon. I was a skeptic, but am a believer now.